This company in Clackamas Oregon can make levers for you. He and I worked out the design and it works but would work better with a small modification. I intend to take my trailer over there soon to show him what I think would work better. It's hard to explain but I know he'll get it when he sees it.
The company is Tri-Fab and their email is: email@example.com
I'll email Aaron to let him know that he might hear from you. The parts are hand made and aren't cheap.
Do your windows still have the tabs that the levers tuck behind to latch the windows closed?