I used that channel to make my car top frame, prior to purchasing my TI.
Drove to the dealer, adjusted the runners to match the vee and drove home with my new boat.
When I purchased a new vehicle, I was able to make further adjustments.
Also used the stuff to make runners for the winch mount.
I can move the car back and forth but wanted to be able to move the winch sideways.
The unistrut was the right price but the cradle wheel setup, of which I needed 4, was expensive.
Works well so was worth doing it right.
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Cheers, Brian in South Australia
Tandem Island -