Replacing camping chair fabric

[raspberrytart]

We have some folding chairs which are great for camping but the fabric on the seat part is starting to split .I am able to sew a new peice on the seat part but the fabric must be close weave shower/waterproofish.
Does anyone know where I can get such fabric?

John Lewis do (or used to) striped canvas deck chair fabric which might work (it comes in narrow widths)

You can buy deck chair/canvas fabric for chairs on ebay, but sometimes they state that it can't be sewn. I don't know if that is true of all deck chair type fabric though.