I wouldn't recommend letting the cat ride in the trailer.
We take our cat and dog with us camping. In fact we took them both on a 5 week, 6,500 mile trip. Catís topping the scales at 20 lbs, dogís about 75 lbs. So I guess I can say we have a large cat too.
I would NOT recommend letting the cat ride in the trailer. Thatís from experience. Once we forget to put the cat in the tow vehicle . We didnít realize it until we were on the road. Stopped at the first rest area to get the cat. Well to say the least, the cat was not in the best of shape when we went to get him, he looked like this
and I wonít mention the other stuff. This was only after about 10 miles.
Moral of the story (and lesson learned); Donít leave the cat in the trailer.
Typically, the cat settles down and rides on the DWís lap. We had a conversion van during our long trip so there was more room. Now we have a truck (CC), but the kids arenít going with us any more, so the dog and cat take over the back seat.