my Stinson my hourly fuel cost has more than doubled (largely due to ethanol in mogas forcing me to 100LL).
Myself and several others have posted on this subject previously, please forgive the repetition but it may make a big difference in this person's case.
Take the !($*%# ethanol out of the mogas.You will invest a little more of your own time, but your time has the potential to cut your fuel bill back in half as you mentioned. It's absolutely earth-shaking rocket science, and only those with a double master's degree in chemistry and nuclear physics can do this....
Put about 15 or 20% water into your mogas. Right from a garden hose. Mix it up really really well. Shake it, stir it, figure out some way to use a drill operated paint stirrer, drive over a really rough road... whatever. The water will absorb or chemically bond to the ethanol like a magnet. Then let the tank sit for a while, until the water and the mogas separate again. After some period of time, there will be two layers : The water-ethanol mixture on the bottom and the ethanol free mogas on the top.
Drain off this water-ethanol, and you are left with un-tested ethanol-free mogas that may meet your mogas STC after testing. Now all you have to do is test the gas for water (per common sense and FAR's) and for ethanol (to meet your STC). If you are using mogas that you tested and proved to be ethanol-free, I believe you are now complying with your STC and your insurance requirements.
The ethanol raised the octane rating of the mogas, and removing it will lower the final octane rating. So starting with premium grade ethanol-mogas will likely be necessary in order to arrive at mid-grade ethanol-free mogas. Please check on the minimum octane requirement for the Franklin because I don't know. The small Continentals are 73, but if your Franklin is 85 or something you might want to ask a real fuel expert what the octane of mogas is before they add ethanol.
Also, removing 5-8% ethanol from your gas means that you have lost 5-8% of the amount of usable fuel. However, you have still saved a very large chunk of money.
Your monetary investment will be a translucent white plastic fuel drum, a drain valve at the bottom (to remove the water-ethanol mixture), some way to mix the fuel, and some way to pump the fuel from the plastic tank into the airplane.
Now the good news... if you have a fuel distributor in your area and are willing to spend a little extra time, you can save a bunch more money by buying the gas there and signing a document certifying that it is for use in an off-road vehicle and not subject to the 30 - 60 cents a gallon road taxes.