The factory tanks used to have some sort of galvanize coating on them. The GM tanks had something like "Long Tern" stamped on them. Not sure if that was a treatment or a type of material they were stamped out of.
The issue with sealers not adhering properly was usually on rusty tanks that were not professionally cleaned before their (usually DIY) application.
The isssue with current ethanol'd fuels is that ethanol, being a member of the alcohol family, attracts water from the air. The resultant gunk sinks to the bottom of the tank as "phase separation".
The reason that many people with pickup trucks went with fiberglass fuel tanks, when gas was really GAS, was to get away from the rust issues of the custom-made steel tanks they'd been using previously. Probably similar for the boat people who also had fiberglass fuel tanks. But all of that ended with ethanol, as it degraded and "melted" the fiberglass tanks, which had to be replaced before any engine damage resulted.
Find some way to "pickle" your new steel tank to keep the rust away. BEFORE any fuel is put into it.
As for baffles, find a fuel tank from a '87-'92 GM pickup or Suburban. Below the hole where the sending unit goes in, you'll see a round plastic baffle. What locates the baffle is a u-shaped strap that is tacked to the bottom of the tank. The two dowels stick up through the baffle, retained by special-coated speed nuts. Get the baffle, speed nuts, and you can probably fab somthing similar to the strap that is tacked onto the tank's floor.
Initially, they only used one speed nut to retain the baffle, but after about 12K miles, the baffle would get loose and (with the force of the moving fuel) wreck the fuel pump unit. The fix? Put the second specially-coated speed nut on the other dowel.
We were told they were specially coated to not rust. They looked just like any other speed niut in our hardware parts selection, but we never had any issues with rust clogging fuel filters either.
Just some thoughts and recollections,
CBODY67