Rather then use the diesel forced air heater while at dock, we have tried to use a portable 220 volt electric heater. To make sure that we had a well protected electrical line, we patched into the separate circuits for the air conditioning heat pumps. (The air conditioners heat pumps can not practically be used at dock side because the compressors are 50 HZ rather then 60 HZ. There is no problem running the air conditioner heat pumps when either the inverter or on board generator are used because both produce 50 HZ power.)
The only issue we have run into is the under voltage that most docks sources have. Where we are now the voltage is about 203 volts. Because of the under voltage the electric heater does not produce it's normal heat output.