I'm away from the van for the next month or so, but if i remember correctly my wheel covers had one mounting point on the top center similar to the ones that hold the panels on the walls. And was otherwise held to the floor by the rubber mat laying on top of it.. I was able to put some dynamat underneath and it fit back in no problem. I dont know if it wouldbe possible to put an substantial insulation underneath and still mount it easily.
Hope that helps havent had the wheel covers off in a while..
148" HR long. 3.5EB and 3.31 ls Premium upgrade package with sync, 10 way power seats, privacy glass, sliding passenger door, with flip out window. Ordered March 6, VIN on April 15th, build date june 5 expected delivery June29-July 3. Delivered! July 3rd.