Some campers have had trouble keeping the boot attached to both cab and cabin, though it's likely still the way to go. However, my 416 DoKa, Camper Mog, had an unusual system that worked very well.
A flange about 6" deep was attached around three sides (left, right, top) of the cabin while an identical flange was attached to the cab. The dimensions of the cab flange were about two inches smaller top-to-bottom and left-to-right than the cabin flange. Thus, the cab flange fit inside of the cabin flange with about six inches of overlap and about two inches of clearance to allow some movement. Some light-duty foam was stuffed in the space to cut down on air intrusion, and little aluminun strips were attached over the intersections to keep out rain.
Worked like a charm. Note that Camper Mog's cabin was mounted in a way that it's front end didn't flex much different than the cab. With a mounting system with more relative flex, you'd likely need need bigger clearances.