Awkward ceiling, including insulation voids.

Hi all. 

My SB uses a cold deck flat roof made with posijoists. To keep building heights down but ceilings high I generally stuffed fluffy insulation into the void of each joist, before fixing solid PIR between them. Then, I attached further 50mm underneath throughout. 

Services run through the joists. My small plant room is where they all terminate, and is a busy place, therefore! 

I now need to close off the plant room ceiling. I cannot use the same method as in the rest of the house due to the mhvr duct runs. 

So, how best to do it? 

I am considering a suspended plasterboard ceiling where possible, but I cannot fit one throughout as the mhvr junction is lower than the highest bits of kit attached to the walls. 

I have considered a net ceiling which I could perhaps cut around all the ducting and pipies, but don't know how or where to start looking for a suitable product. 

Any ideas?! 

Thanks