don't need no stinkin' Rule!
Sorry about the title, I just couldn't resist.
I have made several modifications to my boat and have never used Rule to seal anything. I simply wipe down the area with acetone and use while caulk with silicone. I've never had it peel off or release from the plastic, but if it does (and I've read that even Rule will release), I'll just re-caulk it. I think the key to getting a good seal is wiping down the area with acetone first.
BTW, I also wipe down with acetone before applying the yearly registration sticker to my bow. I've never had any problems with them or the registration stickers lifting off my boat either.
So, my advice is forget Rule and just wipe down the area with acetone and use inexpensive and easily obtainable white silicone caulk. You can probably get everything you need, including a caulk gun, for under $10 at the hardware store.
woodNfish