I made my armor from .10 gauge sintra and used the
hot water method to bend and shape it. From my experience
working with it, I don't think you can get any fine detail
out of it by trying to heat form it. The heat gun should
get hot enough for you to shape it, but if you are trying
to apply dents & dammage, my advice would either use a
dremmel after the shaping...or maybe a "stamp" of some
kind to stamp dents into the heated sitra.
Just my 2 cents.