I also put the brushless motor and 3S pack and copper prop plus universal joint. This is definitely over powered but if you play around with the battery position, it will keep going straight but only for a while.
I ran it in circle and manage to dive it almost at will. The water got inside somehow, so I decided to put an auto-bailer....wrong moves because either the angle was not correct or the one way valve (bb and o-ring) got stuck. It sank and I had to dive in to retrieve it. Later it sank again but it is 40 degree! I had to let it go.
6 months later, I lost a hatch of my other Cat because of the somersault and I decided to dive in...and I found my BL RR2.
I took it home and cleaned it up with plenty of Corrosion X and let it fan dried overnight. The motor, the RX and the esc are still working! I only had to replaced the rudder servo.
I coated those with water proof 3M epoxy DP-270 of course.

http://s7.photobucket.com/albums/y27...P1070637AL.flv