A 4wd Sportsmobile is very offroad capable but obviously we are biased toward the versatility of a 4wd truck & truck camper.
Since you don't have a truck yet I would recommend going straight to a 3500. Even with a pop-up you won't have too much truck for the camper.
"Where do you have to watch out?" Even in the Southwest, with a pop-up, I've had to watch out for low overhanging Juniper limbs. Mostly I've had to watch out for width as the Joshua trees and Cholla stretch out their fingernails along my truck & camper. I've had to watch out for granite as I went through the Needles tunnels (boy was that one tight). I've come within an inch of touching the rear overhang crossing a dry ditch.
"Is it pretty easy to travel this way...how it affects truck handling" Yes, it is very easy to travel this way. Probably very similar to your Sportsmobile. You just drive it like you would a truck. If you watch the weight and don't overload your truck you won't experience white knuckle driving. My wife has no problems driving our truck camper.
I look at Jefe 4x4's list and I see a seasoned camper who isn't afraid to use it. You pay to play rough!