I think you are correct about drilling the hole first. And I am crossing my fingers that the exterior bulge might “heal” but maybe that is unrealistic. The interior bulge is sticking out a lot more, and I’d be surprised if it could be pushed back down. I think the only remedy there is to literally cut that away and replace it with G Flex and fiberglass. One question I have about that is, is one “kit” enough. I don’t think so. Pondering whether to supplement with plain old resin and fiberglass (additional layers) after the kit is used up, or purchase a second kit.
I am not sure what you mean by “plain old resin” but I suspect you are talking about polyester resin. If you get some base layer of G Flex epoxy with or without fabric to bond to the hull, you could use a conventional epoxy such as West System 105 resin and 205 or 206 hardener to bond additional fabric over that layer. Do not use polyester resin. Polyester resin will not cure reliably when applied over epoxy.
As for the G Flex you can purchase the unthickened resin and hardener in kits containing 16 ounces of both rather than the little kits containing only 4 ounces of both. That obviously costs more but the epoxy has a very long shelf life and can be used for a whole variety of repairs around the house apart from canoes. Thickening the epoxy moderately with silica powder is best to form an “epoxy glue” to bond parts together or to form fillets or fill in exposed foam core, but you will definitely want to use unthickened epoxy to bond fiberglass or other fabrics.
When filling in any exposed foam core it is usually necessary to make a second application of epoxy as the mix settles into all the little exposed cells of the foam core. This can be done as soon as the prior application has cured enough that is does not run or sag. The cured epoxy is easily sanded, smoothed, and faired once cured so don’t be afraid to overfill. G Flex epoxy is easy to mix up in batches of any size since the mix ration is 1:1 by volume. Simply mix visually equivalent beads or blobs of resin and hardener by eye.
You may be able to get delaminated pieces of solid PE to conform to a new shape by carefully heating the material but be careful not to overheat.
I am doubtful that you will be able to get the external delaminated material to reconform simply by venting the gas in the void through a small hole and applying pressure but I could be wrong.
Thank you for this info! I will likely go for the 16 ounces of G Flex resin. And I didn’t answer your earlier question about what gas was in the bulge-- I don’t know but I also doubt it is air. Drilling that one hole will need to be the first thing I do as whatever that gas is, it is pushing out the outer layer (along with the inside layer) and at best I won’t be able to do anything to the bulge, or worst, the bulge will expand.