Who would want a radon professional to install your systems? that would cost more than $5

The staining on the framing seems to indicate that the roofer also wasn't at the top of the class. Kozy Kollar should make a roof plug flashing for moments like this. One with a big wingnut, similar to a plumbing test plug.

https://www.lowes.com/pd/Oatey-4-dia-PVC-Test-Plug-Fitting/3880611