I take the servo's apart and put the rtv on all the joints, then put them back together, let it set up for about 30 seconds or so, then tighten the screws. Make sure to put a good blob around the hole the wire goes through. Then you find some rubber o-rings that will fit around the servo horn nice and tight, but not all stretched out. Then put the horn on so that it squishes the o-ring a little bit. You may have to sand a little off the bottom of the horn so it doesn't bind, but still pinches the o-ring just enough to make a seal.
MAKE SURE TO USE SENSOR SAFE RTV ON THE SERVO'S The acidic gas as it cures would/could mess up the cpu board in the servo.
I drop the receiver in a balloon with all the wires coming out of the mouth of the balloon. Then I roll back the neck of the balloon a little bit, put a dab of the silicon on it, gently pull the neck over the blob, work the blob through the wires a little bit, the create a bubble with 2 zipties on each side of the blob to create a good seal.
I do the same with the battery packs that I make. But after putting the battery pack in a balloon, I wrap about 2 layers of electrical tape around it to help protect the balloon against vibration holes. Then I do the same with the neck of it.
Here's a pic of one of my battery packs: