Sorry to here you lost some of your equipment!
I don't know what your bimini cover looked like but the one on my H260 has never even tried to come off either when towing or running along. I wonder if it may not have been done up all the way and the wind was able to catch it?
I trailered my H260 for 8 hours from NH to Kingston, Ontario Canada with the bow and cockpit covers in place without a problem. I did take the bimini down though and stored it inside the boat. Many people have complained that the aftermarket covers don't fit right or the straps are a nuisance and like yourself have seen damage from them. The Four Winns mooring cover seems to be the answer because it has a bungee around the perimeter that hugs the cover tight to the hull. Or as you said, go "naked"! I often take the bow and cockpit covers off at home and trailer down to the ramp but that is only three miles.
Can't help you on the cost of areplacement but would imagine you'll be forking out the better part of $100
