Went back to this thread
Sigh!; still none the wiser. The guy that visited said he had no real idea how to 'finish' the edpm at the edges - but with grp it could be done. ( once he recovered from his obvious shock)
If I'm 'floating' the tiles on pedestals ; why can't I float the parking area also?? on a special purpose construction???
This then solves the issue of car/concrete on grp (or edpm)
Ignoring 'depth' issues - what would theoretically be wrong with say a steel structure to support the driveway?