Wow you guys have been busy, thanks for the support, first off I was interested in Tilemans concept of using HDPE, I've worked with it before and made molds for it but never use it for a structural part.
Nav towers place a lot of valuble gear in what could be very vulnerable places, $300 to $500 roadbook holders, 2 Squadron LED lights @ $330ea, computers, repeaters, all bolted up rigidly to aluminum plates, you go down and the more rigid the mounts the more impact taken by the pricey gear. That's the motivation.
I wanted to test the concept for myself using HDPE just for the side plates, I wasn't worried about front or top impacts, if you do that you've had a bad day and you start over, but side impacts with HDPE and the gear can move, instead of crush or bend and spring right back. That's what I thought Tileman was presenting and after building it and riding with it today I think it has value, and little in the way of drawbacks.
Is HDPE strong, no. Is it strong enough in this application, I think yes.
With fender and tooth lock washers, strict torque values and locktite, I wouldn't be concerned with fasteners, vertically in this application I think the HDPE worked as well as aluminum. Delrin has some nice properties, but it really does have the nasty ability to shatter on impact. HDPE? well?
With HDPE side plates I think the gear will be more survivable in a side impact.
So I'd say Tileman is on to something here. Might not be for everyone, but I'm going to look at it more.