Long Box vs Short Box and slip hitch for 5th wheel

I used a Superglide hitch and it was awesome. Except you can't hitch/unhitch at an angle, which only occasionally was an issue (but a real pain when it was). And you have to keep it lubricated, which attracts dirt, so I got a bed cover. But a dry lube would probably work.

If the relatively small extra weight of a sliding hitch is an issue from a capacity standpoint, then IMO you've got the wrong truck or trailer.