Great idea for experimenting!
Here's two ideas for you to try out as well:
1, make sure your gaps are sealed and there's no excess glue and then use a decent plastic coat primer before spraying with metallic paint.
Or
2, you can use RD65 I think it is to properly plastic coat the foam. This process will set the piece of hard as its causing the foam to soak up plastic and the benefits are more endurable armour that when painted looks just like the real thing.
2 is a long process though. You need to build up about 6 layers of PVA then another couple of the RD65, it's also a bit expensive. But the end result is brilliant.
Go to YouTube and check out Xrobots there's a video of his showing how you do this.
Good luck buddy
That is actually the idea behind it, the problem is:
1) It's expensive.
2) It's REALLY expensive. $90~ upwards for 1 gallon.
So experimentation is hopes in finding a more cost effective solution. *fingers crossed*