1, contact actual loan companies to make sure you can get the loan you're describing.
2, fifth wheels giving you taller ceilings and a more spacious feel. Also usually gives you more storage.
My in-laws have a park model at a campground and love their "Florida Room" (i.e. hard screen porch). It doubles their living area.
I disagree on the no slides. They give you so much more living area. I do agree on the 
I'd also second the recommendation to look at park models/mobile homes. They're usually bigger/taller than RVs and provide a bit more living area.
And lastly, doubly/triply make sure you're allowed to live on your land in an RV. It's illegal in a surprising number of places; people do it, but it's not necessarily allowed. The worst part is that once someone complains and the zoning officer comes to visit, there is no appeal and no getting an exemption.  You must move.