"john west++++" wrote in message ...
car repair fibreglass?

Yes, but just the resin and hardener: no need for the glass fibres. I
think it may need to be weathered for a while just in case there's
something toxic to plants in it. It still won't be proof against
bursting if it freezes solid, though.

I treated some bathroom timbers that way ten years ago, before
painting, and it's stood up perfectly.
[...]
Boat varnish should work.

Won't it eventually lift off? It does on boats :-(

Yes.

Mike.