It really doesn't rust that bad. As long as you keep your tank out of the rain and use Gibbs once every two weeks you are fine. I haven't "sanded" it in weeks and there is no rust on the tank. All it does when it does rust is get mild surface rust, the kind one passover with some 600 grit will cure. I have many decades to go before I need to worry about thinning the tank.
This cold bluing idea sounds quite interesting. Should I do it?
Well .............. it is reversible.
A bit of work,, but reversible.
"IF" you do not care for the finished appearance, you can use a product generically know as "Metal White".
It will strip the "bluing", returning the metal to a "raw" (white) state once again. It will "etch" the metal, but you can get the "brushed" look back again by with your 600 grip.
There are a few different brands of the Cold Bluing compounds.
Each has a different "color", ranging from more "Blue" to more "Black".
The level of "polish" on the steel will also affect the final "color".
You could get rather trick with it and "polish" the tank "differently", versus "uniform".
Give an area of the tank a High Polish, super shinny ........ by buffing it with an automotive buffer until it looks like Chrome.
"Tape off" the area to remain "Shinny" ............. then give the remaining area of the tank a "Brushed" finished by using a Scotch Brite Scuff Pad (Fine).
Remove the Tape .............. degrease ................. then Cold Blue the "Bit*h".
You will be left with a subtle color/textural difference. Giving you a "Ghost Stripe" affect.
I would recommend that you "High Polish" an original style Triumph T100 style stripe................. then Scotch Brite the remainder.
Using Tape will give you a definitive sharp line between the contrasting finishes.
That has potential to be very unique and kewl.
A matching front fender would bring it together, with a stripe down the middle (High Polish stripe, rest with the same brushed finish)
To prevent rust ............ just a simple coat of an automotive "Wax" (sealant) would do the trick.
Again, has potential.