Most campers (the variety with 4 jacks) can be used when off the truck, but some I hear aren't structurally designed to support your weight when the floor is not directly supported by the load bed (or something else).
I don't know if that is the case with your camper, but some people carry the equivalent of a couple of folding saw horses to support the floor so the weight is distributed between these and the 4 jacks. Someone here, forget who, did something clever with a couple of bits of plywood that slot together to form an X, two of which support the camper when off the truck. Doing this also helps prevent sway.
Sway is another consideration - make sure you lower the camper down as much as possible. My camper has the old-style manual jacks held on by 2 bolts each at the top - this makes them much more vulnerable to sway. when off the truck I usually add a couple of saw horses underneath mainly to prevent the sway from causing damage to the jack mountings. Modern jacks which are screwed into the structure along a considerable length of their body won't suffer from this problem as much.
Steve.