So because some one has shared there knowledge about something he clearly knows a lot about that means he's a loud mouth know it all prick does it?
I use ally and hpde a fair bit in my work and I'm not sure if hpde will work I was thinking it might but I'm willing to listen to all arguments.
I like the idea of hpde because it will move in a crash (and hopefully bounce back) it should also absorb a lot of high frequency vibration but I'm not sure how it will go when it comes to bolting/clamping it.
I've seen plenty of hpde sheet split from the pressure of a bolt and washer clamping down on to it.
Maybe using more bolts with top hat collars or maybe using rubber grommets could solve that issue.
Also I think black might be a better color to use for uv resistance.