You would certainly be breaking new ground. The way I see it is if you can get that trailer for $100 then who cares what you do with it the parts are well worth it. Just the charger and trailer parts alone would pay for it. It would be cool to have a trailer for extra storage that had PV panels on the top for power generating. I am sure you could rig some sort of wiring connectors from the trailer to the back of the bus that would transfer the power to your bus circuit. Very cool idea!
Near where I live, a year or two ago, a bomb squad trailer sold on eBay for very little money. Huge heavy "bucket" for bombs to explode in. Oh, the pranks...!
I would not expect very much power from such a small solar panel. But for 100 bucks, the trailer might be a good start for a utility trailer.