This looks good, especially if there is no cab touching under any circumstances.
Is that strips of stair tread friction tape along the side?
If you have 1-1/2 inches total between the wheel wells, why not just drop in the vertical mode, 2 foot long, 1×6’s in the spaces between the wheel wells and the camper base just before you hit bottom.
The other option is to move your centering triangles in a little tighter.
If you need another 3/8’s inch of altitude and slightly more traction, you might try another bed mat on top of what you have already.
The only downside is you must be very exacting and be dead center when you lower the box onto the bed. The camper can be slightly pushed side to side by a 2nd person if it is off a little as you lower.
2020 Ford F-350 XLT FX4 4WD SRW SB SC 7.3L Godzilla Gas TorqShift 10R140 397 amps dual Alt dual batts Frnt Dana 60; Rr Dana M275 E-locker 4.30's 4580/4320/4066# payload 7243# curb wt. 11,300# GVWR 5-er prepped. 2020 Northstar Laredo SC, 12v compressor fridge, cassette, 320w Solar sub zero insulation.