After a long month of working on the forearms, I finally had a breakthrough.
I made just abouth every pep model I could find, just to have as a reference:
I decided that I didn't think that any of the angular models looked quite right, and I decided that it should look more rounded.
So I used different sizes of PVC pipe for most of it. For the front part I cut it into sections and sanded the edges, and superglued them back together to give it grooves:
Once I had the top and bottom PVC sections cut out, I super glued a strip of plastic to hold them together:
Then I took some strips of paper and glued them to the inside of the pipes, and then brushed on some resin to harden the paper:
Then I covered it in Bondo, and started to sand and shape it the way I wanted it to look.
After many layers and a lot of sanding I got the shape I wanted:
Then I moved on to the elbow section that sticks out, and some more detailed bondo and sanding:
I will be priming it and painting within the next few days, so stay tuned.