This sounds like a job for a nutsert set. There are many different sizes of nutserts.
I have a kit and have expanded many a nutsert into steel or aluminum.
I don't see why they wouldn't work in plastic.
pollo
Hello Daberg. Unless you are prepping a collectors bike, just get some flange nuts. Install them on the inside of the rad shrouds with lots of Crazy Glue gel type. then put a few more beads of gel all over the flanges. This set up out lasts the shrouds for sure. Do the same with tank mounted nuts. Put a bolt in the nut prior to glueing to protect threads. Or use the real thing of course. For those, high temp silicone everywhere stops them loosening.