A motor well, is a cut out in the bottom of a boat which an outboard motor is placed into. Some allow the motor to be retracted, so that the lower unit will be protected when the boat is drug up onto a beach. Some are square holes, where the motor cannot be tilted; this type of boat cannot be pulled onto a beach with the motor in place. In both types of boats, the transom is aft of the motor. This type of arrangement is common in beach dorys.
To attempt to build a level bracket for a cooler or generator,, one has to know the slope of the motor well from the horizontal plane. working from the deck is one way, from a level is another way. Just measuring the depth at the vertical "wall" at the forward end of the splash well, and the aft end, does not give this information, which the PO requested. Give it some thought.l