@BritKLR. Very good info, thanks for sharing. I've seen your Tiger in person and have always loved them but I wonder if a Chinook converted to 4x is not a better starting point? I say that based on your experience above. I have not heard of leaks or many other problems with the Chinook. The only problem I have with them is the rear door. The awesome conversion here on Expo (can't remember his name right now) that just got painted is one of the very rare side door Chinooks. Anyway, Ford V10 power, one ton chassis and lots of 4x conversion options.
I'm rolling a 5.3 GMC truck with an older 5.3 these days and loving it though. It seems to me like it would be plenty of power for this rig if the chassis can hold up it's end. I'm kind of bummed to hear of the problems with Provan, I thought they were a bit better built. Still, it wouldn't stop me on this one. If this was close I would go look with intent to buy.
On offroading a motorhome I can say that I've inadvertently done a good bit of it with my old lifted Itasca Cambria and the cheaply built cabinets, etc. held up pretty well.