Do what you think is best.
The tanks came from Honda bare metal 40 odd years ago. There are plenty of them around that are still clean inside.
If you believe that a tank needs a lining, then line it.
My experience is that a bare metal tank, if cared for, has no rust (or any) problems.
Also: that tank coatings cause endless problems. Possibly new technology coatings are less of a pile of crap than the old Kreem et al - but after it fails, cleaning that flaking slimy sh!t out of a tank is a real pain. If you have an irreplaceable tank that's been abused and has pinholes... hmmm... I'd scrap it (or display it on a self) before using a sealant, and find a good tank to use.