[steamer]

Depending on how many channels your transmitter has, just throw another receiver back there in the trailer and plug into the channels you're not using on the tractor. You can link as many receivers to a transmitter as you want in parallel. If you want two dump boxes to go up together just plug the ESC into the same port on both receivers and they'll both work together! Also you'll have to get a BEC to power up the receiver back in the trailer unless you have an ESC for a screw drive or something else
Rob