No experience here with PVC, but I've patched a number of holes in Hypalon dinghies. Once you find the leak, assuming it's a pinhole or puncture, cut a nickel sized round patch and another 3" or so diameter patch. Rough up the hypalon with 150 grit sandpaper where the 3" patch will go.
Pump the
dinghy up until it's hard. Now, here's the trick... using superglue, glue the nickel sized patch over the leak and hold it with your finger for a few minutes. Wear a glove or you'll end up with your finger stuck to patch if you're not careful! The superglue will set and the leak will be stopped. If you can find flexible superglue, that's great, but it's not really necessary. Now, rough up the small patch and apply the 3" patch over the small patch. I use contact cement, but use what you've got - expensive Hypalon cement, Barge cement, Shoe-Goo, etc. You want a flexible
adhesive for the large patch and it really doesn't matter if it takes 24 hrs or more to cure. The superglue will have stopped the leak. But, it's important to apply the 2nd patch since most super glues are not flexible and will crack over time. But, once it's cracked, the top patch will have adhered and the leak will still be fixed. I've done a lot of patches like this on both my
dinghy and on other cruisers dinghies. This method keeps you from having to deflate the dinghy, clamp the patch and wait for the
adhesive to set up before re-inflating.