One of the things I harp about to RV newcomers is to leave your car-buyer mentality at home. Buying an RV is essentially buying a house, with all the concerns of structure soundness, electric power, plumbing, roof & flooring, etc that can apply. Worse, it's a furnished house, so you have appliances and furniture to consider as well. Buyers tend to focus far too much concern on engines and such, but these are little more problematic than the ones in a late model car or SUV. The main vehicle concern with an RV is whether the chassis as a whole has enough weight-carrying capacity to do a good job of supporting the "house" built in top of it.
Think about your living space needs and storage, inside and out. Look for signs of shoddy construction and lower quality materials, especially in a new RV. An RV is inherently a complex and expensive thing to build, so lower-priced models use a variety of short-cuts to keep the price down and hide them behind the bling. It takes a discerning eye to spot quality differences in upholstery and flooring material, cabinet construction, etc. Shoddy or rushed construction is often hidden behind the walls and under the floors where few look. Some of the concerns often found in lower-priced models include loose or unprotected wiring, inaccessible plumbing, cheap fixtures, and poor insulation.