Our cats travel in a Vari Kennel and I prefer it to the folding metal crates like we have in the house for the pup. I've ordered a fabric crate and will see how it does. I was concerned about storing an airline crate when not using it and like the idea of nesting the top with the bottom and filling it with RV stuff. It's a possibility if the fabric crate doesn't work out.
At 4 months old, our 25 lb pup can travel to the vet in the cats' airline crate, but it is for a 30 lb dog and getting a little cramped for him.
I appreciate all the input.