It is going to be a challenge for anything but a light weight camper. As a start check your door sticker for the cargo carrying capacity. You want something like this on the door pillar:
That would give you are starting point. Note you have to subtract the weight of everything you carry in the truck (including people) from this number. Note too that the dry weight of a truck camper is significantly lower than the weight when you add water, batteries, propane and stuff. To get a feel for the difference go here
Truck camper Magazine Buyers Guideselect a manufacturer and then look at the "wet weight". As I noted, Toyota Trucks do not have particularly high "hauling" capacities. Some people say it is ok to exceed your GCWR as long as you don't exceed the axle ratings. I wouldn't do it but I'll let others weigh in on that.