After reading more about the 8500 series, I believe you're right. The system it uses to extend and retract is very simple and the awning is supported much better when it's deployed.
It's true, you do have the support arms/legs to deal with, but that also gives you the ability to dip one corner for drainage in heavy rain, it's much easier to drop completely down for cleaning on the top side, no motors, cranks or winding to deal with, just pull the strap to deploy and release the arm locks to retract. Plus, this is a very common awning and parts are everywhere.
This is the 21' I found...
The guy is asking $200.00 for the hardware, but it was posted 2.5 weeks ago, so I may be able to bargain with him a little bit also. If I cut this in just the right spot, I may be able to make one for the rear also. I would just have to pick up another set of arms, end caps, and fabric.