... I couldn't find it last night night, but here it is ...

https://great-water.com/technical-support/icebox-renovation-help/

Talks about improving the inside of the box with more insulation and a new liner. And keeping the Box "small". If your box is big, I'd certainly consider reducing the size, particularly if you say your insulation may be inadequate. You'll be kicking yourself if you spend lots of money and time with a new system, but you don't improve your box insulation and new gaskets. I've been there.

Also go to rparts.com. They have an article on frog box building. They also are an excellent source for new gaskets. Check out the Box Hatches on their site. Not cheap, but they are very nice.

Cheers, John