WHen these questions come up re dogs in rv trailer. The Dogs WILL let you know there answer. I had 2 malamutes. Usually they rode in the bed in crates. One trip it was 100-105F outside. I put crates over the axel of trailer, put them in there. Checked on them at next rest stop. They were asleep, and did not want out of the crates. Put them there for many more trips. They went into crates without a fuss etc. If they are happy and show it in the trailer, put them there!
With four kids, my ext then crew cab trucks were full of people, no room for 120-150 lbs dogs. One does what one will do with them to keep them safe, sound, happy etc.
marty