You will catch a lot of flak from other campers if you mean leaving him outside in the crate (even with water).
We have a folding crate that fits at the foot of the bed. Blackjack, who must about half the size of your dog, is quite happy to sleep quietly in it when we are away from the trailer. He will bark briefly if somebody knocks on the door or when he hears my truck pull in but otherwise you would not know he is there.
We will put him in there when we pull into a lunch stop and want to go inside to eat. He is happy enough to do it since he knows he will get a treat (french fries or bread bits or something) when we get back.
One other thing: He is used to sleeping in that crate at home as his "safe place".