When installing a new gas tank, like replacement metal, is it necessary to coat the inside of the tank?

Yes, if it hasn't already been sealed. I don't know a lot about it, but have seen kits for it. I bought a used tank from someone and he had already had it sealed.

Someone with some know how on the process will chime in soon I'm sure.

Like the sheet replacement metal from harley or what?

like an aftermarket tank unpainted from J&P

Yeah you're going to have to line the tank in that case. If you don't you'll have problems and rust will be one of them.

me and my homeboy had some bad luck with the kreem tank lining kits

I've heard the same. Some say the lining stuff comes off an gums up your gas. I guess it's a gamble either way.

That kreem us not ethanol safe. Take it to a radiator shop they have the good stuff. Have them pressure test your tank & braze any leaks, then have them line it.

Yes the best way to do it

06 Roadie,
I used this product to seal a tank last year. Easy application and great results.