I've used with great success a product out of Canada called, "PolyAll 2000". I have repaired snowmobile and ATV fuel tanks with it.
It sets up quickly so have it all figured out before you start.
It's not cheap but it works.
Here is the link: http://www.polyall.com
Another product that works great to repair body parts is called, "Three Bond Plastic Repair Kit". You can get this through any Parts Unlimited Dealer.
I use both these products all the time to make repairs and they both work.