Making it out of HDPE should ensure that your great, great, great, great grandchildren have something of yours to know you buy. And it will probably endear them to their Chinese overlords at the same time.
It is very heavy though and quite tricky at times to finish.
If you end up starting from scratch, I recently became a convert to phenolic ply, the stuff they use for trailer beds etc. I used some for remaking floor boards for an Avon Redcrest. It's tough and also has a well textured side for a bit of grip and seeping diluted marine varnish into the edges will seal it very well before a bit of P38 to fill the holes, sanding and a few coats of varnish on them.
It's more expensive than ply but you can usually find off cuts on fleabay that would be perfect for a bench.
