If you want a good 4x4 conversion, skip the Phoenix-Cruiser-Quigley, and send a 2WD to QuadVan.
For a motorhome especially, QuadVan just has superior setup.
1) The QuadVan setup has more travel. The 2" QuadVan option has the same travel as the 4" Quigley conversion. QuadVan also has a 4" setup, which is recommended for off-road driving.
2) QuadVan uses matched 17" wheels, on the stock E-series bolt pattern, on all corner. Quigley uses the F-series SRW metric wheel up front, and leaves the rear wheels standard. Which means you have to carry 2 spares.
3) The QuadVan setup is all Ford SuperDuty, so all Ford dealers keep parts in stock. Quigley uses their own proprietary 5- link, like an older Dodge, which means parts have to come from Quigley.
The E-series is a great platform for converting to 4x4. I have not seen issues from excessive chassis twist. But for difficult trails, the sway bars should be disconnected to improve articulation. Quick-disconnects are optional. If you go with the QuadVan conversion, it'll ride better than 2WD. Of course, the biggest downside of a motorhome is the departure angle. The 23xx seems better than most at least.
If you aren't planning on towing a low (no more than 5,000 pound) I'd recommend 6.2L V8. It actually makes more HP than the V10, and should improve fuel economy a decent amount. And it sounds cool:)