Hey guys thank you very much for the help. I have ordered some smaller drill bits and a centre drill to see if that gets me more accuracy I think I must have been off a little on square and but then tapped the hole square which has then given me a problem I will try the top rails for the other side next at least they are accessible for the nuts if needed.

Neale I think maybe the double skin is a rather good idea. I can get to the ends and weld them but I was wondering does it flex a lot when drilling the centre ? or did you go from the outer edge and bold along to keep the strength at all.

thanks

Rob