When it comes to ABS plastic I go back to the days when I built plastic models and the cement I used there. Best stuff in the world. It's call IPS Weld-on #4. [link]http://www.ipscorp.com/[/link] You can find it locally by finding a glass/window shop in your area. They use this stuff for building with plexiglass.

You use capillary action to apply it. Put you parts together dry, then use a small paint brush (sizes used for building models) to apply the Weld-on to the joint. It will seep into the joint. What it does is "dissolve" the plastic, the two sides blend together, and then it hardens. It only takes about 30-60 seconds to join parts. After doing this I put a strip of fiberglass tape on the back side of the joint.

Now with that said, throw away the ABS and get a fiberglass cowl. The ABS really is weak on the plane and will start getting damaged after just a few flights. Best source I have found has been Stan's Fiber Tech. [link]http://www.stansonline.com[/link] . Yes, it's a little bit of extra expense, but well worth it. They hold up better, are easier to paint, and easier to repair if you do damage it.

When you go to mount your cowl (ABS or fiberglass) use fuel tubing to securely mount it. Position the cowl on the plane and drill a small hole through the cowl and the fuselage underneath. Use a blind inside the fuse. I use 6-32 hex head bolts to mount the cowl. Widen the hole in your cowl (usually 3/16"). Cut about 1/8' of fuel tubing and place on your bolt. When you mount the cowl and put the bolt in it will compress the fuel tubing which will expand and hold the cowl secure. This is an incredibly easy shock mount for you cowl. It will hold your cowl secure, but also isolate it from engine vibration and hard knocks and bumps.

Hope this helps.