Steel Sand Tracking

I'd go for some so-called marine ply, or aluminium - steel sand track is going to use up most, if not all, of your available carrying capacity!

Richard

Or WBP "Water and Boil Proof" from a builders merchant rather than some unknown stuff from a DIY shed. There are some bits of 18mm WBP ply kicking around outside here untreated with an edge on the ground for a year or two they are now starting to delaminate, a bit. WBP allowed to dry out when wet, as it will on roof rack, should last very well.

thanks chaps just an idea.