After pulling the trailer with an old 32" door laying out the back of the truck 48" I made some practical observations along with some math. I'd never set up a tent on a 2.5/12 slope and the rise is 10" @ 4ft. After looking at hundreds of pictures of off road trailer camp set ups, like the ones above, I'm not seeing anyone camping on boat ramp terrain, so the vertical range should never exceed 20" if I parked with the ball of my hitch at the ridge with one vehicle up hill and the other down hill. From experience in the Ozarks where we have hills I just don't recall ever setting up a camp in such terrain. So the vertical range is acceptable even at that extreme.
The horizontal range with 12" over the end of the tailgate, at 32" wide bridge allows the same width as an entrance over the bridge with the trailer jack-knifed at about 45 degrees. Increasing the overhang of the bridge over the tailgate and arching the end of the bridge keeps the corner of a squared off edge moving forward toward te front of the truck, looks like trim to taste and increase the bridge overhang. The door is still centered and there is still roughly 32" of bridge overhang. Basically, no effect from straight to offset.
The bridge can fold down from the front of the trailer, or by detaching the deck and hooking it at slightly different elevations of the door frame on the trailer, the slope is changed to different levels. Could get fancy and employ a jacking arrangement for one end.
Uneven twisting is pretty much solved as it is if the vehicles were detached with stabilizers and blocking wheels, air shocks might be nice. But, I haven't seen camps set up on rough terrain, at least not with trucks and trailers.
So, what's the advantage? Hooking up at the rear vs. the front:
In the cold, wet windy weather you don't need to disconnect the trailer entering from the front, don't mess with the jack stand, hitch, lights and muddy chains.
Quicker set up, drive up and stop, drop the tailgate, lift the top, lower the bridge, pull out the "tube" and zip the door with the front entrance.
Rear entrance, select a site to orient the trailer allowing the truck to back up to the rear entrance, disconnect the trailer, move the truck into position. Drop the tail gate, lift the top, set out your awning and walls, connect the tentage to the trailer and the truck camper.
You could employ a rear entrance like the front bridge and tent tube, but you still have more steps to attend to as opposed to just stopping and connecting. Tear down is in reverse so you aren't exposed as long to hit the trails. I'm guessing the system can be deployed in less than a minute.
You don't have to connect, it's an option, so the truck is still free to use, just disconnect, close the tailgate, drop the top and drive.
I know all about getting out of my sleeping bag or bed getting dressed to go out to the potty tent or facility. All enclosed, just go as you do at home. You aren't exposed and no one can see you anyway in populated areas. (I know some campers will go right out the door but I'd rather not walk in it in the morning).
Pick any holiday camping and boating weekend, in the Ozarks you're guaranteed to have rain, never fails. I'd rather crawl out of bed, move down to the trailer and have eggs and bacon cooking inside. Now, on nice days, lunch and dinner can be from the outdoor kitchen sliding out of the trailer.
IMO, a connection between the truck and trailer is worth the effort. I've never seen this arrangement for any pop up camper or hard side either for that matter. So, why not?
