[carvesdodo]

Pretty much any gussetted / pivotting rack system of sensibly sized materials,you come up with will be fine.

One thing though .... make the boat carry frame one piece e.g. a " H " shape as a minimum.

That way the boat has the two cross bars to sit on and a joiner rail that ties the front and rear bars together.

Without the joiner bar the two crossbars can vibrate independantly and cause damage to whatever is sitting on them.

Worstcase scenario/experience .... a brand new 12' aluminium boat that hadnt been wet .... with 8" vertical splits starting at the gunwhale rail after a gibb road run.