We took over a forecourt that was previously motorhomes, our second forecourt used to be a caravans site. Both went belly up. I've no great insight but chatting to one guy he reminded me that when people look for a Focus so long as condition is fine it'll mostly be exterior colour and mileage that sways the decision once they've found a spec level they like. With motorhomes, for him, it was a discussion about the benefits of a beech interior against another with cherry or mahogany, size and layout of the shower room, upholstery pattern etc...then you also had to have one with the right engine, mileage and history...basically the amount of variables were endless which if you stock it right was OK but one dodgy interior colour or layout and it could stick forever.
Margins seem huge but it's a game you really really have to know your market. We only tried it once and did well but I couldn't do it day in day out. One local said his sales side pays the bills but nothing more but the repairs/renovation side is where the money is.