I designed and fabricated an EMT metal frame to ultimately take a custom fabric cover last year, but decided to shrinkwrap for the first season. My plan was to make the cover before this winter, but will shrinkwrap again, since I did not have the time (or initiative
My experience with the shrinkwrap last year were very positive, no damage to anything, great protection from the elements and ample ventilation with the use of several vents. My frame was designed to allow full walking height, fore to aft and accommodates the ketch rig without unstepping. I only needed to remove the mizzen boom.
Here's a link to a photo album of True Blue last year, published by the framing connector inventor: