If you wrap it round with wet string and wrap it tight making sure the coils are pressed tightly together when it dries it dries really tight. You need to give the wood a couple of coats of the oil as I mentioned to stop the wet string penetrating the plywood as even exterior plywood doesn’t react well with water and make sure you start with a piece of string long enough to do it in one hit. Finish after the last turn by passing the string at the back of the wheel under at least 10/15 coils with a needle and start at the bottom of the wheel as your hand rarely touches the bottom section so you’ll never feel the slight bump of the finishing string under the coils.
Cheers Chris that all makes sense, I think I'll need about 50m of string. I haven't used Tru oil but several coats of exterior matt varnish as I've seen what happens with exterior ply when it get wet. The issue of what to do around the spokes is one I'm still thinking about
