nice design, I like the idea.
what kind and size of fan/radiator are you planning to use for dissipation of 1,2kW?
I have reconditioned radiator out of a V8 and as for the fan I have not decided yet. If I had a backyard I would hire a trenching machine and dig a 10mx10 square 1 meter deep and bury a couple of loops of PEX piping.