Making own fridge need advice


I currently have a Koolatron P20 Compact 12V Cooler that has served me well but is on its last legs. I have found a couple of websites that talk about essentially making the same thing with a generic container.
I have a rampage trail can (storage jerry can) that I want to try and make work. Main reason is jeep + family of 4 gets tight so the ability to store in one of my jerry can holders would be amazing. My question is what is the best way to insulate the trail can? I have seen some insulating bags meant for jerry style water cans but I don't think they will work with my holders. Any think I could put on the outside (tape, glue, etc) that might work?

Full disclosure I know there are better/easy solutions but I am trying to fill a specific niche.