i was thinking HDPE simply for cost. I would need quite a bit more volume of plastic compared to aluminium and to be frank i have more experience with aluminium and weight to strength it makes perfect sense.

Corrosion shouldnt be an issue even though aluminium is extremely reactive it takes a long time ot corrode seriosuly.

Although it may also mean i start a home anodising bath :)

I shoudl add, I am still looking for a suitable plan set ;)