I did a "Build in" on my SlumberCoach.

Used double 1" Blue Styrofoam w/overlapped corners. And Break Metal (Aluminum) to cover the inside with a "Hospital style" wash basin to keep Block ice in.
I adapted an old Freezer rack into shelves inside (not shown).
The real important part was to have a good door seal and a good Chinch lock.
I used a reproduction lock from the old style Ice Box's and a foam weather strip around the door.

http://www.vandykes.com/brass-icebox-la ... /p/205329/I was trying to imitate one of these.

If I were to add up all the cost of materials and paid myself $2 an hour.......it would have been cheaper to buy one.
But that wasn't an option, this one fit.
Happy Trails
Len