I have the same engine - in my normal operations I don't run any additives.
I do have a clear bowl on the bottom on my main fuel filter at the rear of the DP that I watch for water and other contamination. I carry a jug of Power Service that will treat 250 gal of fuel if needed. When I had it in Alaska and there was the possibility of needing to start it in the winter, I treated the fuel before storage. If you needed to do this, make sure you also start the generator so the treated fuel is in it also.
There are several types of Power Service - this is the white bottle with the red top.
There are biocides that can be used if bacteria starts growing in your fuel tank. Some people will use this as a precaution when storing their DPs in warm climates for long times. I haven't so far.
Bill