Diesel Fuel does not do well stored long term, it takes some diligent effort to do so. We have several Diesel tanks and the fuel is treated, but it is used up on a continuous basis. On a Generator I believe propane/Nat gas is best option. We have a couple PTO Gen sets, they are great for working away from live electric source, but they will suck some fuel as we have no small tractors.
If I ever see a cheap 1086 for sale I’m going to snatch it up for just that use. They use less fuel than any similar powered tractor I’ve ever run across. They’re about unkillable as well, and parts are 1/3 the cost of anything with green paint.