UKC

Ello,

I've got a home board (approx 35 degrees) which is suffering a bit in the rain.

Currently it is backed with pond liner and decent quality tarpaulin which seems to be waterproof on the back, but there's alot of accumulation of damp with the wood looking weak and starting to peel around the gap between the boards (I also treated the wood in summer).

It'd be great to hear what advice people have to better protect the wood as I do like my board!

I'd probably get some cheap, L-shaped plastic roofing trim so that it covers right past the edge of the ply. Something like this:

https://www.roofingsuperstore.co.uk/product/grp-90-degree-angle-roof-edge-t...

Make sure the one along the top edge covers the top of the ones running down the sides.

Get a bigger tarp so a third of it can act as a canopy over the front of the a-frame when not in use. Yacht varnish will also help protect it but you will probably have to wait til spring for that now. 

Thank you both, I'll be off to screwfix

I sprayed mine with decking treatment, yacht varnished the joins, and put a thick bead of exterior silicone over the entire edge of the (non marine) ply and in the joints, then lapped polythene plastic over to top. Where I had good coverage it worked very well. Any gaps in the silicone delaminated a bit over time, but it was in a very damp shady corner. The idea of some roofing profile along the edges bonded in place will probably work really well. 

I think your biggest issue is the partially uncovered top, letting water down the back of the ply and through all the bolt and screw holes. Dry it out before watertighting.