cleaning INSIDE plastic rear window

[Perfectlap]

well given your location and the current temps my usual solution won't help you unless you get to an underground heated garage. I lower the top half way and clean the inside of the back window from the side of the car. Plexus then follow up with Renovo.

Regarding your gaping hole better to close that up soon. I would have a top guy look at it. Do it yourself repairs always look messy and you might not get it(glue) to dry properly so that it can lower correctly.