Here's tank that used EN-electroless nickel plating, much more costly than electroplating, but simpler and easier.
https://forum.caswellplating.com/forum/electroplating-questions/10667-plating-inside-of-motorcycle-gas-tanks

https://i356.photobucket.com/albums/oo1/barryadam_photos/IMG_1277.jpg

Paper on nickel electroplating.pdf

Apparently lots of classic auto folks are resorting to nickel plating as modern ethanol petrol corrodes lead in terne steel (tin/lead coating).