With or without ethanol the gas today is more volatile than it was in the 60s; a higher vapor pressure is the technical term. Nearly any US gas today will have ethanol and its going to have more of it unless a new congress is elected. Any system which has no return line to the tank, like the Mustang, is vulnerable to vapor lock. With a single fuel line going only to the engine the fuel in the line can boil and the pump becomes useless. The fuel will not make it to the engine so nothing you do there will have much affect. With the engine running, new cooler fuel helps keep the problem under control but shutting off the engine, or ever idling, allows the fuel in the carb and line to warm. Fuel stabilizer is intended to prevent chemical decomposition over long storage periods and has little, if anything, to do with vapor pressure.
If the fuel is already in the carb and boiling then that is not technically vapor lock. The V8 stock air cleaner intentionally draws in heated air from the exhaust manifold to keep the intake charge at 100F. The carb also sits on a manifold heated by exhaust gas. Both of those were to vaporize the fuel more fully and with today's fuel may be overkill.
Locally we have had 10% ethanol gas in the winter for years but its less of a problem in the cooler winter. Ethanol is now there year round. Personally, my 100% stock '66 Mustangs (both 289s) don't have a problem with the 10% ethanol we now see. In other cars I have had to install an electric fuel pump at the tank to push fuel forward. If the pump isn't sucking on the fuel line then there will be no vapor lock. That solved the problem completely on those cars. An electric pump at the front will still have to suck on the line and would still have vapor lock problems.