The Layout, and the Checklist Before Anything Is Drilled

Introduction

Everything in the preceding volumes reduces to one drawing and one checklist. The drawing is a proposal, not a verdict — it should be argued with once the rack is physically in front of the truck, because a tape measure held against real hardware beats any amount of planning. The checklist is the part that should not be skipped, because each item on it is a mistake that is expensive to discover late.

5.1 The proposed layout

The constraints, restated:

The rack is roughly 60 inches long, matching the 5-foot bed.
The driver’s side is unavailable — the 83-inch awning owns it, overhangs it, and sweeps through it.
Vertical separation is worth ten times horizontal separation, so height differences are the resource to spend.
The cellular array is the receive-critical item; the tri-band ham whip is the aggressor; the scanner is a tolerant victim.

The proposal that falls out:

Table 1 — The proposal that falls out

Position	Antenna	Reasoning
Passenger side, forward, low and flat on the rack deck	Cellular MIMO panel	Low-profile by design so it gains little from height; clear of the awning; forward position puts it as far as possible from the rear whip; flat mounting means nothing to catch
Rear, on an upright or short mast, as high as clearance allows	Tri-band ham whip, on a fabricated ground plane if a conventional whip, or bracket-mounted if the no-ground-plane CompACtenna	The aggressor gets both maximum horizontal distance and maximum height difference from the cellular panel — the two isolation mechanisms stacked. Height also serves its own performance. Rear placement keeps it out of the awning and makes it reachable to unscrew
Passenger side, rear, low	Scanner NMO on its own ground plane	Receive-only and tolerant; accepts the worst remaining position; deliberately not adjacent to the ham whip’s feedpoint
Not on the rack	HF	Rear bumper or hitch if mobile HF is genuinely wanted; better, a wire in a tree at camp
Not on the rack	GMRS, pending a radio	Reserve a passenger-side position; consider a cab-roof mag-mount deployed only when convoying
Not on the rack at all	GPS puck	Costs receive diversity on a shared port; four GNSS receivers already aboard

The two things this layout is buying are the diagonal between the cellular panel and the ham whip — roughly the full length of the rack on the horizontal axis — and, more importantly, the vertical offset between them. If only one can be had, take the vertical.

Where it will need arguing: whether the cellular panel forward on the passenger side actually clears the cab and the tent, whether the rear upright can carry a whip’s leverage without a brace, and whether the awning’s deployed arms sweep further than expected. All three are answered with a tape measure and ten minutes, and none can be answered from a catalogue.

5.2 The checklist, before anything is drilled

Measure and record

Assemble the rack, fit the awning uprights, and measure the finished height to the highest point. Write it on tape inside the cab. Add the height of any whip that will be left standing.
Deploy the awning fully and mark with tape where the arms travel. Nothing — no antenna, no cable, no bracket — goes in that volume.
Measure the actual clear deck of the rack after the awning brackets, the tent, and the uprights are accounted for. It will be less than 60 inches.
Sum the dynamic off-road load against the 450 lb limit: awning 64 lb, plus tent, plus hardware, plus everything else. Confirm the rooftop tent under consideration still fits the budget.

Decide once

Confirm the cellular antenna covers 600 MHz on its datasheet, not on its marketing. An antenna starting at 698 MHz is not a rural antenna.
Confirm the ground-plane independence of any antenna relying on it, on the datasheet.
Write the connector gender at both ends of every run on the drawing, and order against that list. SMA-male to the gateway’s cellular ports; RP-SMA is a different thing.
Choose the coax entry — existing grommet first, one well-made bulkhead second. Find it with a flashlight before buying a hole saw.
Decide whether GMRS gets a permanent rack position or a temporary mag-mount. Do not reserve rack space for a radio that has not been bought.
Decide whether HF is mobile or camp-only. Camp-only is cheaper, performs better, and removes the hardest problem in this dive.

Build in the right order

Fabricate the ground plane plates before drilling anything. Scuff the anodising under every mount and every bolt.
Bond the rack to the truck body with a proper strap.
Mount everything with T-nuts so positions stay adjustable. Nothing gets drilled into the rack extrusion or the truck body except the one chosen coax entry.
Seal the entry from both sides, with a drip loop below it. Prime and seal every bare-metal cut.
Fit ferrite chokes at the feedpoints before deciding they are unnecessary.

Verify before calling it done

Sweep every antenna in place with the NanoVNA. Resonance and match on a bench mean nothing; measured on this rack, in this position, is the only number that counts.
Run the desense experiment from volume three: RSRP and SINR quiet, then per band at full power, then at reduced power, then with the whip raised. Record the table.
Re-measure the finished height after everything is fitted, and correct the tape in the cab.

5.3 What the first season is for

None of this is final. The T-slot exists so that positions can change, and the honest expectation is that the first year of use will produce two or three moves — an antenna that turns out to foul the tent, a cable route that chafes, a whip that is fine at 26 inches and hits a branch at 44.

The thing worth protecting is the irreversible set: the coax entry, the holes in fabricated plates, and the height record. Everything else is meant to be revised, and revising it is a sign the process is working rather than that the plan was wrong.

5.4 What to record as this gets built

This dive should grow a sixth volume once the rack is physically on the truck. The material worth capturing, in order of how hard it would be to reconstruct later:

The measured desense table — unique to this vehicle, and unobtainable from any source but this truck.
The NanoVNA sweeps of each antenna as mounted, which will differ from the manufacturer’s plot and are the baseline for noticing that something has changed.
The finished height, and what it cost the first time it was forgotten.
Photographs of the coax entry and the ground-plane plates, because those are the details nobody documents and everybody wishes they had.

Antenna theory, measurement, and the individual antenna types are covered in the Antennas project and are not repeated here — theory-and-practice for fundamentals, portable-mobile-monopoles for mobile whips, discone-wideband for the wideband receive case, baluns-ununs for common-mode current, random-wire-end-fed and multi-band-dipoles for the camp-HF option, and nanovna, analyzers-vnas, and power-swr-field-strength for measurement. The radios themselves are covered in the Radios and Scanners projects. The gateway, its antenna requirements, and the buy decision are in this project’s Cellular Gateway dive.

References

Xtrusion Overland — XTR3 bed rack specifications: 1530 aluminium extrusion, T-slot profiles, 450 lb dynamic off-road / 850 lb dynamic on-road / 1,550 lb static.
Topoak Overland — 270° awning: 83 in “Wide Shade”, 84 × 8 × 11 in packed, 64 lb, $649; 98 in “Extra-Wide Shade”, 74.3 lb, $849; 4 in corner clearance required.
RadioReference and KB9VBR — mobile antenna spacing practice: quarter-wave minimum at the lowest frequency, roughly 19–20 in at 2 m; NMO ground-plane guidance of about 6 in at UHF and 18 in at VHF.
Isolation versus separation geometry: roughly 20 dB per decade horizontal against 40 dB per decade vertical for stacked vertical antennas.
FCC — human exposure to RF fields from vehicle-mounted antennas.
US amateur, GMRS, and 3GPP band allocations, for the harmonic table in volume three.
Coaxial attenuation figures for RG-58 and LMR-240.