Remove the straps and ropes and replace each one with a bungie cord in about a 6" loop. Buy bulk bungie and cut your own. Where the loop ends, pop rivet in a lashing hook. Avoid snaps like the plague. Install rear facing vents on the cover so the material will be naturally drawn down tight as you travel, with no flapping. Look at a PWC cover and use that as a guide. You won't believe how good it works.
An extra plus side is that when you get to your vacation spot and decide to moor the boat for a week, the cover will still fit very nicely and you won't need the trailer under her to tie the cover straps to.