It's no problem at all, friend. Just to clarify, this is the product we use: https://www.amazon.com/Grabber-318111-No-Coat-Ultraflex-Flexible/dp/B07DX4STXF/ not that stuff from the tv infomercials lol. You can bend it in the middle to match the angle of your corner. It comes in a big roll so you can just roll out as much as you need and then just put it on with some mud just like you would with normal tape.

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If you have any other questions I can help with just feel free to shoot me a pm or something :)

Hi there, I do drywall for a living so maybe I can help here. Is there anything behind the insulation you can still screw to?

Its always hard to tell just by pictures, but I suspect if you are able to fit in smaller pieces of drywall in those gaps as you were saying, and get everything screwed down good and secure, you can use a product called flex tape. We use this stuff at work all the time for these sloped corners. It has either hard plastic or metal inside the tape depending on what brand you buy, which keeps it very straight and rigid. Even if the drywall is all crooked and not lining up like yours is, this stuff will basically make a new straight corner for you.

This stuff is usually pretty wide, 5-6 inches I would say? It can cover up small gaps of a few inches but anything bigger than that you would definitely need to try and fill in as much as you can. The tape will cover it up, so it doesn’t even have to be pretty, just as long as there’s a good backing there. Small pieces of drywall you can screw down or even a quick set mud to fill in the gaps with would do the trick