Quote Originally Posted by ptjw7uk View Post
Using box section why not bolt right through your only problem then will be collapsing the box with to much tightening!

Peter
if you do that you never get the bolts to stay tight. There is a solution to this.. drill through the bolt size then get some tubing whose ID is the bolt size and open up the reverse side hole to the tubing OD. the length of the tube needs to be the inside dimension of the box plus one wall thickness. Then you can bolt through with a washer under the bolt head, the tubing is strong in compression compared to the box section and prevents it crumpling.