[Archers] Target making question

[Craig]

So I'm coming up on my first event where I am the archery marshal and 
have to design my shoot.  I've got some good ideas for shoots, but I 
need advice on making the targets.

What I'm thinking of doing is making a framework out of 2x4 that can be 
assembled on-site and disassembled afterwards, for transport and 
storage.  It's basically a framework similar to the door jamb of a 
doorway, except wider - about 5-6' in width.  I want to use it for not 
only hanging a flat target inside the opening, but also a spinning 
target (think burlap sack with 2 target faces).

Regarding my targets - I'm thinking of a couple of targets that are 
basically foamboard with paper targets attached on one side.  Foamboard, 
insulation, that kind of thing.  What would be reccomended for that 
(thickness, etc)?  Should I have something behind it to help stop arrows 
from going too far through it?

As for the hanging target, I'm thinking burlap sack (assuming I can find 
one) or a box (of which I have plenty).  Reccomendations for what should 
be used as filler in those to help slow arrows down and preventing 
blowthrough?

Thanks!

-Cian