Ok, I finally found the time to get back to this project. I found two computer fans, hooked them up in series so they are slow and quiet, and built an aluminum frame for them. I took my 12v
cord with switch and ran the cord from the bathroom where it plugs into an accessory port above the closet, down through the closet, behind the stove, to the area under the sink, where I snaked it through a gap between the cupboard and the fridge. Then I screwed the fans to the back of the cabinet above the fins, and added a piece of flashing to direct all the air up and out the vent.
It runs, it's quiet, and it makes a gentle breeze. Probably the only downside is you turn on the fridge fan at the switch in the bathroom, which should confuse future owners someday. Now I just need to level the trailer so I can run the fridge and see how it works. Hopefully we'll have a fridge that can actually be trusted to keep more than pop cold this summer!