This past weekend allowed time to work on back section of harness. The backpack harness came with aluminum convex strips sewn into material for support. These strips are how I am attaching everything together with machine screws and other aluminum brackets.
Eventually the back section will enclose the battery bracket and have windshield/dash attach over battery. So far overall weight is approximately 10 lbs. Battery will probably add about 5 to 10 more.
One inch PVC pipe will be more than sturdy enough to support and hold back assembly together.
My initial idea for doors to attach was using aluminum one inch strips and then bent to desired angle. With PVC couplings I can get any angle I want and have a design that's able to remove doors with ease for transport and/or storage.
You can see in this photo how much the doors weight down the back assembly slightly, might have to adjust to compensate.