Buy the offroad diesel and you'll save about 40 cents a gallon. A 55 gal tank of diesel can run that size generator for a week or so (or double that if you want to be selective with time and circuits). You can store more very easily. Since I use diesel for my tractor and UTV, I always keep a couple hundred gallons around in transfer tanks (and re-stock when prices are low, certainly NOT now).
Although I didn't do it, you can integrate a couple hundred gallons of diesel storage into a rectangular tank that goes under the generator mount. So the whole setup is very compact. The other benefit is that it's an 1800 RPM water-cooled generator, which has a much longer duty cycle and service life than the 3600 RPM air-cooled propane/NG Generacs. Those Generacs are popular, but you can burn through their lifecycle in just a couple hurricanes.
I was oblivious to a lot of the benefits of diesel generators until we got soured on some of the issues putting in propane and then diesel turned out to be a great option. After seeing all the hassles my neighbors have dealt with for propane over the years, I feel lucky we didn't get caught in that trap. To me propane really only make sense if it's indispensable for a 1-2 things and convenient for some others.
Anyway, not trying to be a salesman here, but you mentioned you needed propane for a generator and based on my experience that should not be a reason to hold out for propane. Like I said, once we realized we didn't need propane for that, it freed up a lot of other constraints and issues revolving around propane.