The sides are hinged to fold down. The sides are probably strong enough but the hinges may not be strong enough to tie the camper to. You might check with the bed mfg. to see what they say their side rail hinge can handle.
If they don't rate the hinge strong enough or you aren't comfortable with the specs, you will need to use some type of tie down that connects to the bed or frame of the truck. I think I would probably weld couple of heavy D rings to each side of the bed. That would allow them to fold down when you aren't using them.
I have seen some who tie the camper down with ratchet straps like those used on tractor trailers. They have a hook that would go under the edge of the bed. You would need to be careful not to tighten them too tight.
I think the pressure that Fastguns put on the camper, when installed per the instructions, is about 300lbs.
