Before leaving this evening I used some cheap sealant to try to block the ends of the aluminium tubes that support the wheelhouse roof. The flies seem to use them a lot.
I’ve also resealed where the electric cable currently goes into the cabin (when we switched to the new consumer unit the foam tile was left with a bit of a gap).
We have caught a hundred or so flies with the fly paper (mostly outside). Inside the “electric zapper” fly swat has been effective, must have killed 40 flies with it). Overall when there are large numbers of flies the little Makita vacuum has been the most effective, catching hundreds.
Hoping for fewer “friends” when we are at the boat for half-term!