I have a normal Tom Tom and combined with my Iphone's mapping system and especially the map on Gas Buddy, with a little common sense, and following signs that warn "no trucks" or "no semi's" I've never had any problem getting into a spot, except twice. Tom Tom took me down a flooded road once and I got stuck in the back of McDonald's restaurant parking log and had to back out. I think in 30 years of camping and RVing (me and the wife), that's not too bad.
I don't have any info specific to the RV versions, but I did find this article. Based on this article, if I had to choose one, I think I'd select the Rand McNally. I like the feature it can switch to different flavors of RV's or normal auto. Although the article is a couple years old, it's worth reading at least once.
Click here.