I'm not going to touch the camper off for service comments. That depends entirely on the service facility and if or not the vehicle has to be placed on a lift and how much overhead clearance the shop has.....
...and, cabs on late model Ford Diesel pickup trucks are routinely removed for engine work, not hard to get off and working on the stuffed under the firewall engine becomes much easier. In fact, if you have a perforated head gasket or any head related issue that impacts the passangers side head on a Late model Ford pickup, the ONLY way to remove the rear head bolts is to remove the cab. Conversely, timing chain replacement on a light duty F series eco boost engine (F150) requires cab removal as well, again, not a big deal.
On to the rest of the OP's post about the shifting TC in his bed. Campers shift for a number of reasons. One is the bed is slippery. A rubber bed mat or a spray in bedliner like Rhino Liner goes a long way toward planting the camper securely but, no matter how good the bed liner is, if the camper isn't secured properly with the tie downs, it's likely to shift, especially in an off camber situation so...
I'll probably get some flak here on my comments but...
I don't care for Tork Lift tie downs, especially the front tie downs. The problem is geometry. You are exerting securing force (through the tie down turn buckles at a splayed angle relative to the tie down plates on the camper itself, IOW, the tie downs atttach to the Tork Lifts in a plane outboard of the edge of the camper itself (Imagine a inverted V). That allows the securement force to spread outward and any loosening of the tiedown's become amplified. If the get loos, they get really loose and allow the camper to move in a lateral motion opposite the force applied. Not so much with the rear tie down's because the angle of pull isn't as splayed out.
Why I run HappyJac tie downs on the front and Tork Lift on the back. The Happyjac's allow you to exert the securement pull in a near vertical or slightly inward plane so the camper is restrained from movement. I use the Tork Lifts in the back because I prefer them over the HappyJac bumper buttons as they are more rigid than the ends of your bumper, but that is the only reason.
Been hauling truck campers for many years, off road and on road and I've never had one shift in the bed. The only time I've had one crooked, is loading it crooked.