The whole drilling (or pun intended "hole drilling"?) thing worries me. I'd rather have door panels removed if need be than to drill and plug. Waxoyl is pretty famous stuff in the Land Rover world - and something I've been thinking about doing. I don't believe their method is to drill - rather, I believe they just use what ever existing points of entry are present and mist the internal panels that way. Rovers North
http://www.roversnorth.com/ is the main distributor in the US of the stuff.
Shaun