Hi,
First off, water can enter between the two hulls, run a quick bead of CA around it, just to make sure it is perfectly watertight. The transom area, particularly pushrod seals is also a common area for water to enter, so keep them well packed with grease. On the EX, with the hatch only being held down in the middle it tends to flex up around the edges, and not stay as tight as say a Villain IV 's hatch where the hatch is held down from the four corners. This cant really be fixed, some foam around the edges of the hull might help though. With electric boats, auto bailers are generally never used, the reason is because you want to focus on keeping the water out in the first place, not getting it out, as electrics and water dont mix. The use of them on Villains has been to try and remedy the poorly sealed hatch, like I said, they are generally not ever used or recomended on electrics, but in this case one wouldnt hurt. But thats not to say that you can give up on trying to get the boat as water tight as possible, you still want to keep the water out, that is more of a last resort. Hope this helps you out a bit.

Chris