... that is the most important part of any frig redo. Next comes the gasketing. I'd get these two things in order first. If in fact your box is large, I would add vapor barriers, seal the box, add a layer of 2" polystyrene (I think, can't remember what's best here) foam all around the inside, the foil backed R5-6 per inch stuff works great, seal all that in, fiberglass & gel-coat over that so you have a nice new completely sealed inside box. Then add your cold plates and systems.

There are dozens of articles on the web how to go about doing this.

Absolutely talk to Cleve. He's great. Better yet take a trip to New Hampshire and go see him at the Shop and design everything, he will show you what you need to install it by yourself.

Cheers, John