I think it really depends upon the personality of the animal. We have a couple that have no interest and I think we'd be pulling them out of every corner and hiding spot in the rig. We have another that taught us that camping with a cat was just fine.
We started with a harness but she hated it, the collar worked out pretty well (we're very very careful so we don't strain on her neck - they have different anatomy from dogs). Heeling and walking on the same side of trees/fence posts took some time but cats are as trainable as any other animal - just have to figure out what their drive is (cats are mostly food driven). She is also play driven, fetch especially.
Here she is in the "dog days" of summer, relaxing and enjoying a beer with me.
/Jeff