Large transport cage while traveling is how my folks did theirs, and free to roam about in their trailer.
With Yuki, we've been getting her used to be on her harness in the yard (she's not allowed outside without it), and once the new camper is done being built, we'll get her used to being in it with her cat box and what not.
She's riden with us in the pick-up on several occasions, and usually likes one of three places. On the misses lap, sitting on a perch in the area behind the front seats so she can watch out the window, or hunkered down on the seat to sleep.