The one thing that I remember doing when I paint-balled was to get some material that I liked. Ideally something rather light weight.
Then go to an arts and craft store and find some Mastic, I think it is called.. You can spray I believe the fabric and then place it on the weapon, or vise versa. Make all the seams line up on the bottom of the rifle, so they are out of sight and out of mind.
When you are done you can cover in another layer of the spray and then you are good for a long while.
I would defiantly try it on a small cheap thing first.