Does that water end up under your feet and traveling down the seats into your sleeping area?
Like Graham, I've never had a problem with water flowing forward under the tent from the cockpit on my GRP BR20, although the floor might get wet and so it pays to keep sleeping bag and stockinged feet off the floor. I forgot to bring a sleeping pad on one trip and slept direct on the side bench, so even i would probably have noticed a puddle.
It's a good idea to keeping a pair of thick-soled crocs handy for midnight-visits requiring walking on a wet cockpit floor to the bailing bucket in the stern. BTW, NEVER pee over the side, I believe the RNLI have a special acronym for bodies found with zips undone...
I've not experienced wet sleeping bench misery in Bill's Askari, a wood-epoxy BR20, either. It may be that a largish outboard motor, fuel and other kit in the stern helped slope the side benches towards the stern. I also had a thick self-inflating mattress and military grade goretex sleeping bag cover so maybe I just did not notice any damp. Incidentally, after I broke Askari's batten for supporting the sleeping platform we ended up sleeping just on the side benches. A bit narrow but doable.
Ability to resist wind damage or distortion is quite high on my list of desirable tent attributes for undisturbed slumbers, so I'm not a fan of flimsy tents.
I've just thought to also mention that it's handy if the tent is not so long it blocks entry to the cockpit at the stern, or has a side-entrance. Otherwise mizzen mast pole-dancing is necessary to get into the boat from a pontoon.
Matthew
Gladys BR20