Gadget for Top Case

In a week or so, I'll pick up my new motorcycle at the shop where I got my scooter last year. I love the 180 cc scooter, which is fast enough to get on the highway and economical to ride for commute. But it's not strong enough to ride over the passes to get to the east side of the mountains, or go to Portland or Belingham. So I decided to upgrade it to a motorcycle with a 750 cc engine. It's called Nevada Classic from Moto Guzzi.
I already have a 45 l top box on the back of my scooter. It happens to be big and wide enough to put my handmade field easel and a 12"x16" stretched canvas inside. I'll put it on the motorcycle once I got it. Now I need a mechanism to hold wet canvas in the case. The one in the photo can hold two canvases. Then I'll stack the easel on top of it. That's my current plan.