I would agree with others who suggest larger or additional tanks. This is IMHO more important with propane than with diesel.

Bulk propane tanks cant be readily filled from smaller containers without specialist equipment becuase the contents are pressurised.

Diesel is easily handled in an emergency.

Tanks should be sized for the worst resonably forseeable power outage, and time without re-supply. This is likely to be about 96/100 hours, not the 72 suggested above.
Consider power fails at 14-00 on a Friday, preceeding a holiday weekend. You cant order more fuel for some hours, since the outage might be only for an hour or two, with little fuel consumed and therefore limited room in the tank for more.
If the power is still out on Teusday morning, then more fuel can be ordered first thing in the morning, but probably cant be delivered for some hours. That is between 96 and 100 hours after the power went out.

It may be possible to obtain diesel fuel from retail filling stations and transport it in jerry cans, drums, or vehicle fuel tanks.
Dont count on it though, remember that a widespread outage may affect the filling station which needs electricity to pump fuel.
In the event of any widespread emergency fuel is likely to be in short supply.