I'm new here, but have built my fair share of large gun props. I built a full size Killstick from the webcomic Megatokyo, I helped in building an Ork Shoota from WH40K, and a few others here and there. There is a few things I would look into..
1. Reinforce the top carry handle and around the rear carry handle. If you think it's strong enough... make it stronger. People are going to want to pick it up and pose with it.
2. To help with the weight of carrying this beast around, make a concealed strap that attaches to a belt. It will allow your body to take the weight instead of your arms.