On Windburn the external rails are held down using SS hanger bolts. They are convenient to lay a bead of butyl around while installing. So far ( 17 years ) no concern with strength.
The inside rail has a long screw that goes through the cabin top and into the external rail. Michael Brown Windburn C&C 30-1
_______________________________________________ This list is supported by the generous donations of our members. If you wish to make a contribution to offset our costs, please go to: https://www.paypal.me/stumurray All Contributions are greatly appreciated!