To my way of thinking one of the primary advantages of the pop-up TC is a lower profile and lower center of gravity to negotiate more difficult roads. That said, you would probably lose some maneuverability with a side entry unit that has a big rear overhang.
Departure angles mean a lot when traversing dry wash beds, particularly if it's a long bed crew cab. I think the flatbed idea has worked well for some, but make sure you are realistic about what kind of off-road capabilities such a rig would offer.
MANY comments have been made through the years on the pros and cons of all the manufacturers you have listed so I won't repeat any of it here except to say my next pop-up TC will come from Hallmark.
Best of luck.
