Looks like a thin steel bumper with an aluminum cover (rivets in the end). But either way, probably not strong enough to support over 100lbs bouncing down the road.
I take all my rigs to my favorite welding shop and have the rear bumper replaced with at least 1/8" steel 4x4. End caps will still fit. They also reinforce attachment to the frame and build a proper platform. Get estimates and I think you will be surprised at the affordable cost. And then you have no worries about strength
Scott and Liz - Southern NM
2012 Wildcat Sterling 32RL - w/level up (best option ever)
2007 Chevy 2500HD 4dr short bed Duramax w/allison
Reese Fifth Airborne air ride king pin coupler with Sidewinder