Pretty certain the windows were the main culprit. I temporarily fixed them with duct tape, which seems to have worked, judging by the lack of puddles this morning! That will have to do until summer, when I'll take the windows out and re seal them.
Boards above the engine aren't great, so I think that's the main source, but will check the stern gland too (it DID leak slightly but was fixed.) Will get a tarp asap in the meantime.
Not at all adverse to hard work and/or mucky jobs, I just asked about the Aquavac on the offchance. But, I guess towels and nappies it is!
Thanks for your advice.