On the side of your "little white bucket" there should be a piece of wire connected in a bracket in a U-shape. This "wire" is the temperature sensor, and should lead to a little dial controller (usually labeled 1-7). Turn on the fridge. Do this at the dock
, as it will run full time until it gets cold (which may take several hours to all day depending on what's in it, temperature, etc.). Once it gets cold (how cold depends on where you have the dial set, I find 2-3 for fridge temps, 5-6 if I want a freezer, depends on your insulation) it will start to cycle on and off to maintain the set temperature.
The fact that your evaporator is frosting means it seems to be working. Check the tubing from the evaporator where it comes out of the fridge box. At most you should see frost on 1-2 inches where it exits the box. More than that indicates a refrigerant charge problem.