I’ve started work on the frames for the sides of the roof now. Below is my solution for fitting the wheels (I’ve decided to use just four as they’re supposed to be good to carry 250kg each and the entire roof shouldn’t come to that much).
Getting the 3m lengths of tube into the pillar drill to make the holes for the bolts was awkward. Not as awkward as it would have been if I’d extended them to their final 3.6m length first however.
I’ve ordered some stainless bolts, washers and nyloc nuts for the final fitting of the wheels as they’re bound to get damp and avoiding rust on the bolts would be useful.