This looks as good a place as any to discuss some of what happens when you recover from inversion in a GRP BR20. Better here than the locker seal demilitarised zone anyway!
When I turtled, unballasted and solo, in the Fal in 2015 and once I was the right way up again, I had a list to port and an enormous amount of water in the cockpit sole. I hadn't heard of Matthew's excellent tip of removing cockpit sole water double-quick by opening the inspection hatch into the empty ballast tank (and the tank being empty was why I capsized in the first place). I'll certainly try that trick if (when?) it happens to me next time. On that occasion I did lots of pumping with my transom-mounted Whale pump.
The list to port partly sorted itself out as the port ACB tank emptied itself into the outboard well but there was also a large amount of water in the port locker, which had come in over the unsealed locker rims fore and aft. Photo below, soon after righting, with the wind coming over the starboard side.
I think it might be worth installing a port locker drain in the vertical wall of that locker, at the point where it is just above the level of the cockpit sole. A non-return valve or flap might protrude into the locker, or the cockpit, or both and be another source of potential leaks into the locker in wet conditions. What about a simple and robust large diameter captive bung, as used in the sump at the back of the boat?
https://www.ronstan.co.uk/marine5/product.asp?prodno=RF294. Just unscrew it and let most of the locker water drain away into the cockpit (and then into the ballast tank) while you attend to other matters, like stopping your oars from floating away. There would still be a bit of water left in the locker where it is lower than the cockpit sole but I don't think it would be enough to produce any sort of list. If you eventually sailed off on a port tack, the heel to starboard would get rid of more water. You would just need to remember to screw the bung back in when it had done its job.
I think this would be better than what I had to do on the Fal, which was to open my starboard locker to find my hand pump, then open the port locker to pump the water out. Luckily for me and for the other BR20 that turtled, the sudden stingjet, katabatic downdraft or whatever it was that flattened both of us quickly blew itself out. We could therefore sort ourselves out in weirdly benign conditions. It wouldn't have been a good idea to have been opening lockers in a high wind.
