I have a Westland cover and want to reinforce the area where the support pole sticks up into it but I haven’t found any suitable patches. I was thinking of using to iron on patches and sandwiching the cover between them but all of the reviews that I found said they peel off in no time. Any techniques or products you can suggest?

I have always had a piece sewn in to do what your describing but I have done temporary repairs that turned into about 8 months before I and the canvas shop had time to fix. Go to Sailrite they sell tear-aid tape for canvas and Dacron tape may be an option. I used tear-aid I cleaned the canvas well and let dry it was still in place after 8 months. I realize your not repairing a hole but a couple overlapping pieces of tear-aid may strengthen the area

Sailrite also has canvas how to videos

That’s really helpful info - thanks!

Kill 2 birds with 1 stone. I do not sew around the vent. I just cut a little hole to fit the vent through and then tighten. It's lasted 15 yrs so far.
Watch the video.

My dad installed 3 of those vent/support things on his pontoon cover....its been going for 10yrs now! previous cover lasted him 4yrs before the poles ripped through. He also cut the holes himself but he took a piece of copper pipe the same size he needed for the hole....took it to the bench grinder and sharpened the edge then took a map-gas torch and heated up the end and cut through the cover material. His thought was it will singe the edges and keep it from tearing later...hasn't failed him yet so it must have worked