I used a tool to fit threaded inserts to fit the exhaust and air intake. Here's the silencer:

The intake has a silencer of some kind. Not sure if it makes much of a difference...

I placed the silencer and exhaust where an electric loom used to be. This was relocated on the crossmember:

Here's a picture of the D1 underside (the non-working heater). It is mounted on an aluminium plate fitted on a piece of plywood, the overall thickness of these is the same as the plywood floor plus floor insulation (= 2cm). This means that the heater is flush with the floating floor. On the underside, there is a 2cm recess. It's grey on the picture, as i've sealed it with underfloor sealant to protect the ply.
