OK, I know this is a long-shot, but do any of you DIYers happen to own a plastic welder? This is on-topic, because it's for my bike trailer. Appropriate compensation would be supplied (materials & beer?)
Nope. Plastic welder gear costs $$$$. Go for epoxy and pop rivets, cheif. The hardware store might put in your rivets for you if you know the right shop. They do it in Skokie at the Ace.
Only other way to bond pieces together at home is fiberglass. Smooth it out with Bondo or body filler. Remember to install solid plastic angle pieces at the corners or some kind of similar bracing - like aluminum 90 degree angles.
Yeah, my back-up plan is pop-rivets for strength and silicone to seal up the joints. It would just be much more elegant to weld the plastic. Harbor Freight has some fairly cheap ones, so I tho't some tweaker around here might have one. :-)