So this is the roughest possible sketch I could muster of an idea I just had. It seems like its too simple to have not been tried, but.. oh well. K so the idea here is that you have two grav lifts, one beneath the "door" (dumpster on a strict track) and one at the top of its track. For simplicity's sake, we assume that it's not an issue that there's a grav lift right in the doorway you're trying to walk through. In a practical demonstration, everything here would be doubled, the dumpster would lie on its side, and the two grav lifts on the bottom would be on either side of the doorway not interfering with people walking through. Whatever the case, the idea is clear - one set of grav lifts has the power to push the dumpster up to the top of its track. The other set can push it downwards. Alright. So in the simple example there are two grav lift spawns on the map. We set the run-time min to 1, and the run-time max to 1 as well. Thus there must always be a grav lift on the map. Next to each grav lift there is a fusion core ready to explode. The fusion cores are at instant respawn (equal min and max). The two switches are some sorts of mechanism that when activated, fire a fusion core forward. Then each one of these switches is aimed at a different grav lift / fusion core - either top or bottom. So when you activate one switch, a fusion core blows up the, say, top grav lift. The grav lift has 10 seconds to respawn, but the game is told that it must have 1 grav lift on the map, so the bottom lift spawns and pushes the dumpster up. Then 15 seconds later I want to close it, so I activate the other switch. The bottom grav lift is destroyed, and the top one spawns in lieu of its brother. The dumpster is pushed back to the ground. I imagine that in both cases the dumpster will be actively pushed in to the ground or floor. As long as the track is tight, it will stay securely in place, but it will jostle around a bit. Hopefully this would work to keep the dumpster "disturbed" and keep its disappearing timer from starting.