I have a CTEK D250S mounted under the bonnet (hood?). It is on the drivers side (offside/right) behind the brake/clutch servo I think. UK spec vehicle. I can provide photos but it doesn't get too hot there and I've not had any problems.
It was in my last D2, and I've had this one now for 3-4 years now, and the one before it was fitted for at least a year.