I do statistical crash analysis for a living. The data is collected on the crash reports and it gets into the database but I've never had need to dig into it for work.
Trying to say one type is safer than another gets messy really quick. As others have said driver age and experience can play a big role. Maintenance is another big question. A great many RV's are not kept up sitting for months at a time.
I would expect negligible differences assume all types are well maintained, kept within appropriate weight ratings and you take extra care driving until you know how they perform.