MVHR cold loft insulation shed/igloo

Hello! I was wondering if anyone was able to share photos if you have built a frame/insulation shed/igloo for your MVHR unit, especially if the unit is suspended from the frame?

We are retrofit installing in a cold loft bungalow (not ideal but no other options sadly). It’s a Zehnder ComfoAir 180 Luxe with preheater and enthalpy exchanger.

The plan is to build a frame (still working on the design - any suggestions would be amazing especially for an alternative to the counterbalance beams) from CLS to suspend the unit and both manifolds (no gable walls to hang the unit from). Then wrap OSB then PIR board, not sure yet whether it needs to be airtight or not?

The ducting will then travel down inside the ‘igloo’, and exit below loft boarding/within the loft insulation layer across joists (each duct will also be individually insulated from the ‘igloo’ exit point too).

I’ve seen this recommended a few times but I cannot find any guides/visual examples, and the exact details are throwing me a little bit!

- Even though it’s an insulated box, will it still be cold inside or will the heat from the mvhr unit be enough to keep it comfortable (ours has a preheater if that makes any difference?)

- Not sure how to PIR insulate underneath without impacting the frame, it cannot be a continuous layer as the frame is going to have to be secured to the joists and counterbalanced so it doesn’t fall with the weight of the unit. I believe the PIR has to be on the outside rather than the inside of the box, though it would be much easier to get a continuous fit.

- I’ve read mixed things on airtighting. We have put an airtight membrane down on the loft floor, up and over the joists but below the insulation level. Not sure if we need to include the ‘igloo’ in this airtight layer (remove membrane where the ‘igloo’ sits, then up and over), or if that would just compromise the layer? Or do we airtight the ‘igloo’ as it’s own separate entity? I’ve also read that the unit needs airflow and ventilation, not sure if that’s needed from outside the ‘igloo’ or if it’s more about making sure the unit has breathing room and the frame isn’t flush against it?

- For the door of the ‘igloo’, again how best to make sure we can access the unit without compromising the insulating properties?

If anyone has done anything similar, advice would be much appreciated! Thank you!