I suppose if you used a back board over the thin RV walls to spread out the weight you can mount a HDTV as big as you want. We currently have a 26-inch size in the living room area and a 22-inch size in the bedroom area. We use the VIZIO HDTVs inboth room so that when I can't find the TV thumper I hopefully have a working spare in the bedroom haha.. Personally I would think a 32-inch size HDTV would be as big as I would want to watch in the living room area.
these are sample mounting back boards from google