Walk away, cig smoke is one of the most difficult smells to get rid of.
Not only the smoke but tar and other leftovers of second hand smoke will have coated every inch of paneling, drawers, cabinets along with every nook can cranny..
One of the most disgusting things I hated back in the days of repairing consumer electronics was when a customer who was a heavy smoker brought in a TV or stereo.. It smelled up the shop and it coated everything not only on the outside but the inside.. Took a lot of hard work to clean up and still smelled, but at least when I was done the customer thought it was a new unit..
There ARE a "surplus" of used RVs, in other words there are more used RVs than buyers, go and find one that was not smoked in.. You WILL be happier.