Got a fan?

Got an iron?

I got a box fan in the shop. I turn it on and do the shrinking in front of it. The shoe on the iron can be applied so it only touches a small area of the covering. Shrink a small area at a time.

When you cover a hole in an open area, you need the patch to stick far enough away from the hole that you can apply heat that doesn't soften the outsides of the patch while you shrink the patch that's over the open hole.

Apply any patch with the low temperature recommended by the covering mfg. Let it cool completely. The idea is to get good supporting area around the hole. When it's completely cool, turn up the iron and touch only patch area in the hole area.

When the air inside the "drum" heats up and expands, the fan blowing on the other side will cool will carry off most of the heat.

I have had to punch a hole in one bay that was a real problem. I did it in a corner where the covering was supported by a rib going one way and the LE going another. I didn't get heat close to it and when everything was worked out and cool, a very small patch went over it on low heat without any trouble at all.

It's a technique you learn over time.