So this was my first major cock up on the build, thankfully it's only inside the battery/heater compartment and not on the outside!
The manual states that the heater needs to be mounted as high up and as far outboard as possible which makes perfect sense. I started by dismantling the heater so I was left with an empty box with no ends on, four M8 rivnuts (I would have used M6 but the nozzle for my tool is broken) were installed ensuring the bottom two wouldn't fould the heater matrix.
I then made a cardboard template which was offered up as high and outboard as possible, holes marked on the bulkhead which were then drilled out. I then put the two outlets back on the box and made sure they fit which they did, great I thought.
What I didn't consider was the fact that when the matrix is back in the outlet pipes protrude inboard and prevent the whole assembly going high enough, so my holes are too high.....doh!
These will need filling and I'll start again....