At this point it comes down to stiffness. If you double a materials thickness, you quadruple its stiffness.
Now a sheet of 3mm HDPE and a sheet of 3mm Hardox... yes, the hardox is stiffer. But with 25mm HDPE... yeah, no contest.
Also remember, something many people forget, Hardox is designed to bend! Its designed to be formed into scoops and buckets so in combat it will bend if hit hard enough.
Go HDPE. Once you have got your design resolved and have a few competitions under your belt, then you can upgrade to Alu bulkheads :-)
