Help. Under carriage plastic flapping. How to seal?

The large black plastic that covers the insulated undercarriage of my TT constantly comes unhooked and begins to “flap” or hang down. It used to be one long contiguous piece and was screwed in at the corners to hold it in. At some point, I had some work done on the black tank pipes and the repairman cut an approx. 5’x5’ piece to access the area. It was sealed back up with “100 mph” tape and that held for a little while. Ever since, I have struggled to find a way to get it to stay sealed. It doesn’t take long for it to start hanging down toward the road.

I’ve tried gorilla tape, “100 mph” tape and neither seems to work for very long. Does anyone have any suggestions on how I can get this sealed up for good. It is thick black plastic, butting up against the same thick black plastic.

Rivets? Some kind of NASCAR tape? “200 mph” tape? (not that I can get going quite that fast in my 5.3 v-8…..

Any Suggestions?

Sorry that I don’t have pics.

Thank you