It would probably be a good idea to take a look at your insurance policy to see if storing it voids the policy.
As a former Fire Marshal and Arson Investigator, I'd say that it's very unlikely that your home insurance policy has any specific language about storage of relatively small (like 50 gallons) of gas at your residence. BUT, there might be some very crafty small print somewhere in the policy that gives the company an 'escape clause' for contributing factors in the event of a fire. (How many of us have more than 50 gallons of gas inside a garage? Between my truck, car, motorcycle, small mower, riding mower, emergency generator, and two five gallon cans, i have about 65+ gallons in the garage tonight...)
But the cautions about HOA's and local zoning ordinances could be a problem, depending on the locale. Besides being an ex fire service guy, I also worked at one time delivering products for a small petroleum bulk plant in Nevada. Had a ton of customers with 150-200 gallon storage tanks on racks (outside) at their homes/farms. That was a pretty 'normal' thing back in those days. But that was mostly a rural situation...if that's your case I don't think there would be much concern. :whistle
We had a 300 gal tank at the farm. This was back in the day of no ethanol in gas and our tank was filled by the local distributor twice a year. Never had a problem.
I fill up my 6 gallon plastic gas cans  every month.