I am using a roof thimble for 4" pipe, and 3" non insulated stove pipe. Sheet steel with a one inch air gap on the walls behind and beside the stove.
I have a sheet behind it now, the same distance from the stove as it will be in the camper. Temp in front of the sheet is 130'F, temp behind the sheet is 68'f. So that should work fine.
It is set up now almost exactly as it will be in the camper, so only some minor changes might be needed once in the camper. I am glad I was able to test it all out before install, it would suck having a hole in the roof and finding out I need to change my set up.
So it's been running out in the garage for 9 hours now. It seems to be holding the garage at 20'c (68F) and it is -1'c (30'F) outside.