Hi Salty,
Yes this problem is worrying and I think most responsible boat owners are concerned about it.
I bought my Bavaria last year and moved it between the first and second lockdowns from Cornwall to my mooring in Suffolk. As there were many years of antifouling on her, I left things as they were and made the passage. I found that whilst in Greece in my old boat the fact that the boat was moving most days, just a light coat of A/F was fine and did the job.
The main reason I did not antifoul this year was because of time constraints ( the virus) and also that I wanted to strip the boat below the waterline later and thought adding more was pretty well a waste of time!
You would be amazed at how little crud was on the hull after she was lifted out at the end of October!