Jim, we are on 12 years or so on ours. We have not found a great patching material. We heard of a club in NM that was using roofing emulsion. I admit we have not tried it. The best thing I have found is contact cement. One of the guys had some he used to sheet foam wings and it worked pretty good. It is still hit or miss and I can't really tell you why. We only patch once a year. Some patches last a couple years and some blow off in a few months. All done at the same time the same way. The only thing I can figure is the ground just holds moisture longer in some places. Ours is down on dirt/clay not grass, and it will stay damp for a week after a good rain.
Second best thing I tried was 30 minute epoxy. It will hold the patch a year or so. If it is a big spot, like from a crash, just staple a new piece over the top. When I say staple I mean use the 6" turf staples like ours is held down with.

Good luck, David