Support rails for trailer

[Pastor]

I'm in the process of building a trailer for my little inflatable. I have used parallel twin rails to support each tube similar to the snipe trailers. These are made from 1" box section. What can I use to cover them to protect the boat? I've thought of the obvious pipe insulation but even the 22mm size is too small to fit properly over the box. I would like to get this sorted before I take the thing to be galvanised in case I need to drill for fitting