Blue Seas has a great line of waterproof circuit panels and other electrical devices for Marine and RV applications. No relay build in but easily added.
A little less waterproof is the Painless Wiring Unit called the Circuit Boss. There two units have relays build in just add power and accessories.
Make sure you fuse the power source wires and as close to,the power source as possible.
I am glad it was mentioned about a circuit panel i was thinking along this line but it slipped this old mind but now I put it on the list... "Add waterproof, relay controlled, circuit panel for tractor lights and Seat area".
Thks