I only use bondo on parts that are meant to be smooth, the thing with H4 armour is that there are so many little details and nooks and crannies that it would take a long time to sand out the detail with a dremel. Also i use epoxy putty to fill in holes and gaps in the pep. My forearms are quite long but skinny so i had to leave the pep file almost the same length, i had to cut up the sides and bring them closer together, then i used bondo to smooth over them. So yeah you're basically right.
I'm going to fibreglass the arm loop, then pour rondo down the support into the shield part. as well as the standard resin on the outside. Hopefully this will be enough, but if not i will have to do a couple layers of thin rondo on the outside.
Thanks