I think if you were going to make a truck camper work for your family, and wanted to be 100% sure of being within the safe limits of your vehicle while still being able to bring enough stuff/supplies to have fun, you would probably want to at least have a 3/4 ton truck, if not a 1 ton. You could keep a running tally of the weight of everything in your truck and do this, but you will probably find that your Toyota's payload rating would severely cramp your fun, or cause you to take risks with your family's safety. I wouldn't rule out getting a truck camper for your family, as I could easily see kids not minding setting up their tent and sleeping in it. Kids should be doing that anyway, it builds character. But you would probably need a bigger truck.
That being said, most people who use a lighter truck for their camper install a swaybar and rear air bags. These items don't increase the legal payload rating of your truck; that number is set when the truck is born. They do increase the amount of weight your truck can carry logically, but not legally. Some state troopers/highway patrol/provincial police do carry portable scale units for investigating issues like accidents and illegal hauling. My wife and I went this route when we first got our camper and were putting it on a 1/2 ton truck. I also installed bigger brakes. But we still had a scary incident of brake fade while going down a long incline in the sierras. Over time, I imagine an overloaded 1/2 ton will start to wear out more than it should too.
Like others said, the mounting system and ability to be in the camper while it is off of the truck are completely dependent on the camper.
