"glue" and toilet paper? Same orientation as fiberglass matting fabric and resin/gel coat. Build up to the thickness/strength desired, machine/finish as needed.
When we got the first flexible bumper fascias, 3M came out with a repair kit. Sand the split, fill it in, sand like a bondo'd body panel, paint, etc.
There are some plastics that Super Glue won't glue, by experience. Then I later found out that a dusting of baking soda would make it work.
ONE trick that a guy from another car club demonstrated to us one day . . . at the hobby shops, they usually have some clear or colored plastic and a kit to take a mold of a small item for reproduction with the new material. He used it to do some smaller round tail light lenses with (on a '40s car). Put the basic mold material in the holding fixture, then add the item you're taking the mold of into it, then add more molding fluid on top of it. Let it all "dry" or cure. Remove the "assembly" from the holding fixture, carefully cut and separate the pieces, remove the original part, then use that mold and the new plastic to make a new lens. It worked quite well, including the casting ID and such.
Plastic welders have been around for about 20 years now, maybe more like 30. I first heard of them from people doing restorations in the 1980s, when repro plastic parts hadn't been done yet. Probably have to hold your mouth right the first few times?
CBODY67