I'm trying to install some defrost ducts in my car, but space is very limited. The standard molded plastic fittings are just too big.

What I have to do is fabricate a very low profile duct sytem myself that would hug tightly underneath the dash and cowl so I will have room to run the AC ducts. The defrost exits the unit facing the firewall, and it's about 6" forward from where the defrost will exit the duct through the dash.

I want to use some sort of plastic similar to what the condensor unit is made from. I can use the flexible duct to turn the 180 degrees to get the airflow headed back toward the dash, but from there i want to use plastic. From the collector, it will be about 4" before it has to split into the individual ducts - which I'm thinking about using something like 1" X 1.5"w rectangle tube.

Does anyone have any tips about what material to use, where to find it, and what type of glue would hold up?