We did this about 3 years ago - Traded our Ford Excursion (tow vehicle) and 34' Citation RV trailer in for a Class A Motorhome (see signature). Very happy we did, too.
We did not do it for the reason alluded to here (lower monthly payment overall). We did it because we wanted a Class A and all the advantages it has over a towable RV. That, and we wanted to travel to places further away, and really liked the advantages a Class A MH has when on the road longer.
RV dealer actually took both the truck and TT in on trade when we did this. They gave us very good tradein $$ for both, too. They were very happy to get both - they sold the TT within just a week or two, and liked the truck so much, they kept it for themselves and use it to haul parts, and move trailers around.
..Doesn't seem lke this would be the best move to make if one was wanting to reduce debt, expenses. Would be extremely 'short term' savings at best.