I found a place under the sink in mine where I hung a 12-volt canister-type vacuum. Put a hose down to the kickspace by the floor and ended it with a plastic flange for the hose. Hard-wired it, so that all we have to do is pull out a flexible hose just long enough to reach everywhere in the trailer. Kind of like a central vacuum on the cheap. With the long hose the resulting suction is pretty weak, but enough to suck the dirt up fairly quickly.
Good part is that it is always available, works even when boondocking
, and doesn't take a lot of juice from the battery
. No carpeting on the walls though.