Bruce, I once had to come up with a soft tonneau for a client with your same concerns about permanent attachments. What we ended up with was six tension points at the stake pockets by using flush-cut wood stakes and hairpin-style hood locks. I installed stainless "eyes" in the vinyl cover to slip over the pins under slight tension. In order to keep the edges from flapping and stripping the paint, I sewed magnets into the perimeter at 4" intervals. It looks like a fat, slightly boxy welt strip, but I wanted to make sure the magnet was strong enough to hold on with a layer of vinyl between it and the steel. It actally seems to hold better than snaps, although the truck it's on doesn't go past 60 mph so we don't know what speed will pull the magnets loose.
edit: I remember him telling me he once forgot to set the hairpins on the rear corners. He didn't make that mistake twice, as the cover flapped once and, uh, nearly ruined his seatcovers.
If I were to try this again, I think I would have more magnets (closer together) on the front and rear edges, for such "senior moments."
