I have split and resealed about 10 tanks using Gasket and SealAll method.
The option of using only a sealant without a gasket may be an acceptable
alternative and certainly less complex.
I am working on two early Kiekhaefer Mercury single cylinder gas tanks at present
The first one had warped seal surface, which has been dealt with
The second tank has a split gas outlet boss and a split in rear corner of top half.
In taking tank apart I noticed that tank had been sealed without gasket using a Goop like substance. Tank was not easy to open so I guess the answer to your question is Yes it can be
done with good results without a gasket.
I will use a gasket and SealAll onntank #1 as I have had good results, more time and effort ,but, I am pretty sure I will not have to do it over.
Tank #2 I will grind seal surface of flange. Best repair would require some welding and possible distortion stress. So maybe more sanding later. Epoxy gas tank repairs I have seen
appear temporary fixes ,however , no distortion. Cost is also a factor.