I've had incredible results using CLR (Calcium/Lime/Rust Remover). It's incredibly cheap too. When cleaning your tank why did you allow it to sit without any fluids in it? When I'm done cleaning them I immediately rinse them out with water, put a few rags inside of the tank and blow compressed air through the whole thing, pull the rags out, then leave the air blower inside of the tank for a few minutes. Fill it with gas, slosh it around, drain that gas and discard, put fresh gas in it, boom done. Your tank shouldn't be sitting exposed for more than a few minutes, otherwise flash rust is inevitable. Some sort of lube or oil would work pretty well I imagine to stop the flash rust, but that stuff will settle eventually and you'll be back to where you're at now.
I've never cleaned by electrolysis. Honestly if you don't mind waiting a few days and some elbow grease, CLR will do anything you ask of it. Haven't had a tank yet that it couldn't fix. And FYI it WILL pull KREEM out if you let it sit long enough. We had a Road King in a few weeks ago that had KREEM applied OVER rust and it was causing all sorts of issues with the FI. The CLR pulled out the KREEM as well as the rust underneath it. Looked like a brand new tank when completed.
I'm going to try some tests with some fluids and see which works better as I've been wanting to try to clean with electrolysis for quite some time, and I am not short on rusty parts to clean. Will post results!