Plastic welding, yes solder iron method works ok. There are a few others but try looking up friction welding on youtube. You said you already have some plastic welding rods which I'm guessing is 1/8" diameter. Slide some in a dremel, bevel your material edges and have at it. The dremel will friction weld the 2 pieces together while melting the rod. Go back and forth or circles like real welding. I did this to my gto intake setup on my ls3 swap. I hope this helps, glue route may be easier too..
Does anyone have any advice or guidance for welding together ABS plastic? Anyone have any idea what the proper chemical adhesive might be? I'm guessing it's a solvent based chemical that "burns" into the plastic but I don't know for sure.