Welcome to the forum, Mark.
We have an Espar forced air diesel heater. It runs best on #1 fuel oil
[or kerosene or jet fuel, but that costs much more, and we use our heater a lot...]
It doesn't like old diesel, or any additives. Either are just asking for maintenance
issues [which will cost you far more than fresh, clean fuel of the correct type.]
While we are frequenting higher latitudes, we keep one of our two fuel tanks
dedicated to #1 fuel oil
for the heater. We also installed a separate external fuel filter
dedicated to the heater- preserving the smaller filter built-in to the heater. This set-up works well for us.
In an emergency
, if we run low on #2 diesel for the engine
, we can transfer some of the #1 to the engine tank and add something to give it more lubricity. [per our engine manual. e.g., Marvel Mystery Oil.]
If you do this check your engine manual for what, if anything, would be necessary to burn #1.
Best wishes with your new boat