I must confess I have not used Fuel Dr, but was advised by my diesel mechanic to use this, and all has been well.
Chemtech: Fuel Additives
And I let my tanks sit less than half full for ages and hardly ever change my filters, (because they don't seem to need it), but I believe the fact my tanks are linked and always self-level and both draw from the bottom of the tank, is probably my best protection. (Nordhavn also follow this principle I believe), as I hardly ever have more than a tspnful of water from the primary fuel filter bowl, and the engine never runs rough - ever. Oh bugger, I've probably jinxed myself now….