I would say yes, the NEC definition of structure is "That which is built or constructed".
Chris
Chris, along with the definition of structure, the structure needs to be served with power as well. The exception to 250.32(A) does not require the electrode system if the block heater and charger are equipted. If the enclosure had a sub panel then yes it would be required but the gen set is only an output. The OP needs the GES because it's a SDS.

Rick