Problem with the roof thing is that you'll be fucked if it rains

Boot mounting rad is deffo a good idea. As I mentioned before in this thread ; have you spoken to Tom Scarlett as I am pretty sure his car is in bits at the moment and he did it to his S1 with no problems.

Tom and his Dad did it themselves and are very clever

Maybe he'd be able to offer you some advice on potential problems, better ways of air flow and anything else they encountered along the way.

It doesn't hurt to ask