The water heater safety relief valve will weep and drip a little. It will run down onto the compartment door seal and can leak into the compartment. With changes of outside temperature the water can evaporate, then condense on the compartment walls. Check your compartment door seal.
It is normal for the relief valve to weep a little now and then. The water expands as it is heated. If all of the faucets are closed, the relief valve will weep to keep the pressure from going over 150 psig. On our Sunseeker, when this happens it's almost impossible to flush the toilet without opening a faucet first. If you ever have a stuck thermostat the relief valve will pop fully open at 150 psig, then reseat when it gets back to a safe pressure.