"I currently use soft throwovers and they hang really badly and get wet and are destroying themselves on the tops of the rear shocks."
Hi Steve,
I had exactly this problem with a pair of soft throwovers used on my Bullet cafe-racer, so I cut up some stout cardboard to fit tightly inside as reinforcement, assembled with parcel tape. For experimentation, I made one with the end of the internal box to hinge open, and the other with the side to open - both work quite well. I also fitted simple brackets to enable the pannier bases to be held by cable-ties to prevent them swinging out when cornering.
I've since found some ally slotted angle (vintage 'Dexion'!) and will assemble this to make internal frames that'll be even more rigid than the cardboard.
It wasn't really my idea, as I was simply trying to reproduce the very effective shaped plastic 'formers' fitted inside the 'Ducati Performance' soft panniers on my Monster.