One other comment, this one about raising the camper in the bed of the pickup.
Alaskan Campers set me up with four 2x2s running crossways in the bed to allow air to circulate and dry the plywood underfloor of the camper. They have been selling and dealing with wood camper issues since the 1950s, and quite a few of their campers historically reside on the wet coastal areas of the PNW, so they likely are well versed on the options.
A solid piece of plywood in wet climate used to raise the camper can/will wick water/damp up to the underfloor plywood base of the camper, causing wood rot over time.
A rubber mat as described in this thread would not wick moisture, but neither would it allow air to circulate to dry any moisture that finds its way into the plywood base of the camper. The rubber mat might work well in dry climate, but I would personally be hesitant to use it in wet or humid climate, especially if the camper is stored outdoors on the pickup.
This is something that maybe worth consideration for long term camper integrity...?
I'm not an expert.. I'm just along for the ride.