Sorry, but I would not put my dog(s) in the bed of a pickup.. open to weather elements. Puppers in fifth-wheel not an option with heat even if stabilization of kennels could be done. Dogs loose in fifth-wheel? No way. I was following a trailer in a nearby town the other day, they took a right turn and the entry door flew open.
My dog has the whole back seat of truck, built up so he can look out the window or lie down. On the floorboard, up to the seat level, I have "stuff" stored.
Rearrange stuff or board then looks like only 2 options to me.