I have corrugated roofing plastic sheets. I use those.Cardboard is handy for taking viscous off mainly
Very hard to get wrench In there without damage if they are stiff.
Just take your time with the cowl they can be brittle
I try leaving the fan on.
I have no tools to take it off and I guarantee if I take it off more work appears .
I have 3 cm space when moving the plastic cowl back. That should be enough sliding the rad out and the new one in.