Bob, the Espar D2 has no water heating capability and thus will not be able to provide block heating. It is an air to air heating system used to heat cabin air. It uses a fan to move the air. (I can imagine a setup involving passing hot air over a air to water heat exchanger but this would be highly unusual in a SMB. With a D5 as part of the system it would be redundant)
The D5 has a chamber in which water is heated and a pump or pumps that will move the water (normally engine coolant). A flat plate heat exchanger is normally used to provide domestic water heating for your sink / shower. The flat plate keeps the coolant and domestic water separated. I do not have a D5 but am pretty sure winterizing normally involves draining the domestic water out of the system but leaving the coolant able to flow through the D5 and the coolant side of the flat plate.
That is a typical layout, but there are variations, so I would need more info on exactly how your setup is installed to say if you can run the D5 as a stand alone block heater with the Domestic water loop closed/drained. There may be valves which need to be set to alow just the coolant from the engine block to flow through the D5.
Beastie 3: 2002 7.3 EB Cargo: Agile TTB, CCV Mid Top, Custom Walk Through, Lots of stuff added. BlingMyRig.com