You can check for other threads on this site that discuss whether or not to use a gasket between the mount plate and the wing and the sender and the mount plate. I've spoken to people who have used each method and if done properly either works fine.
For the wing to mount plate interface, assuming you use the supplied cork gaskets, I'd suggest putting pro seal on both sides of the gasket all around and also on the screws as you tighten the unit down. Once cured, do not turn the screws to tighten them any further -- the turning action may break the seal and create the very leak you're trying to prevent -- I know, I've done it. This is true whether you use a gasket or not.
For the sender unit itself, you might have the supplied thick rubber gasket. Again there are those who argue for using it and those who argue against it. My original installation used the rubber gasket and I spent a lot of time chasing leaks. I could stop them for a while and then they would come back. The trick on installation, I believe, is to not tighten the gasket so hard that you mushroom out the gasket. One mechanic told me he likes to use the rubber gasket but said to avoid putting any lubricant on it as that will soften the gasket which leads to the mushrooming effect and that promotes leaks by elongating the gasket holes. I finally removed my rubber gaskets this year and found the holes around the screws had become oblong and thus let fuel leak around them. So I pro-sealed the senders directly to the mount plate without a gasket. I haven't had any leaks since. So for my 2 cents, I'd not use the rubber gaskets.
Good luck.
Chris
