[LeftOverParts]

Casters on carpet just seems to be asking for trouble with a lot of friction. You might consider adding a vinyl strip where the wheels run (or an all vinyl floor).

If you keep the carpet, another option is to potentially float the bed frame using those 6 x 6 furniture moving glides for carpet or something like them.

Or, as Foldbak's link shows, rollers attached to the floor. However, as mentioned previously, the rollers on the floor make it so the bed frame is cantilevered when the slide is closed which would stress the connection at the wall or at slide floor if L brackets are used. I added the same rollers at the end of the bed frame to eliminate the cantilever. So far, no impressions in the vinyl.