Alternatively if my foam method doesn’t work I’ll be getting one of these which are specifically designed and proven to do the job.
This is the new Jules Plenum Shield (copyrighted) which needs no tools or expertise to fit.
It is manufactured “in house in North Wales” from a high quality BLACK plastic.
Laser cut for a good fit and appearance.
It’s concept is a “Fit & Forget” part that will extend the inspection intervals for the plenum chamber.
ie: Ideally only every 1-2 years or whenever you change the pollen filter.
Read more and buy here at …… https://www.the75andztclub.co.uk/forum/showthread.php?t=68328