Why not just strap a compression dry sack over the rear seat? They hold a hole lot of stuff, though maybe not the kitchen sink, and will keep your gear dry in the most severe of rainstorms. I've used bungie cord, or ratchet straps to tie it down, haven't had any issues with either method. An added bonus is it doubles as a nice backrest for you on the interstate. I've got this one and it works great as supplemental luggage. http://www.seatosummit.com/product/?item=eVent+Compression+Dry+Sack&o1=0&o2=0&o3=291-12 For $30 it's a hell of a lot cheaper than replacing your softbags. Food for thought.