Let's do some calculations.
First, we have to estimate the bottom price? Let's be stupid optimistic and say $2 p/gallon savings.
Second, how much fuel do we want to hoard? Let's be stupid and say 500 gallons. So we are assuming we are going to save $1000. It might take us two years to recoup the investment? That's assuming 250 gallons per year??
Third, how much will it cost us to purchase the necessary equipment to do this venture? Probably going to pay $500 for a storage tank. Another $100 to rig it up with a hand pump? So we invested $600.
Fourth, our potential profit is $400. It will take us 24 months to realize this profit. So for the next 24 months we will potentially save $17 p/month.
Fifth, would we borrow the money to do this venture? Probably not because the payback is so low. So why would we do it?