I guess the first thing to find out is what your friend is visualizing. If he is thinking of a really basic, very compact pop-up, for use hunting and four-wheeling in the back woods then there are models that weigh very little and will sit happily on a short bed F150. If he is thinking about something larger and more luxurious then he should be starting with a different truck.
Payload weight might not be his biggest problem if it is the HD version of the F150 ecoboost - in the right specification I believe that can have a payload approaching a 3/4 ton truck - but he would need to check. The length of the load bed is the real problem, and apart from those tiny ultra-light campers I mentioned he will find very little that fits. I might be the only person on this forum with a 5'9" load bed. My Shadow Cruiser sticks out over a foot at the back, and it is a really short camper (no bathroom). My camper is over 20 years old and is not much over 7' long at the bed, but when I look at literature for modern campers they all seem a lot longer (8' plus).
Steve.