Hi,
I know you posted this a long time ago, but we also travel with a Maine coon who wants out!!! We solved this by a two prong attack. First, we got him a harness (kitty holster on Amazon) and we take him for long walks. Sometimes he will walk a hour, which is MY limit. Second, just before bedtime we have an energetic play time. I get him to race around the RV. He loves to blast from the back to the front and back again. I reserve special toys for RV trips, so he gets something unexpected to play with on trips. I reallly work to wear him out before we turn in. He then gets some treats and after treats he curls up for a big bath and bed. AND do NOT declaw (amputate his toes) him. It isn't necessary!!!