Probably. Just don't sit on the very foot of it.
We put a queen size Sleep Number bed in our 325CK Cruiser Patriot fifth wheel this past summer shortly after we got the trailer and were very comfortable on it. It hangs off each side by about an inch and off the foot of the platform by maybe 2 or 3 inches. The mattress that came with the trailer was a pillow-top and it wasn't terrible, but we knew we wanted something in there that we could count on for years, and the original mattress just didn't feel like it'd be that great a couple of years down the road.
There are a lot of folks on the forum who have put memory foam mattresses in their trailers and love 'em. Lots of people who just got memory foam mattress toppers, and they seem happy, too.
Good luck.