Building a new boot cowl

I’m building a boot cowl and was wondering what kind of sealer to put between the firewall and new sheet metal ?

silicone is all atlee uses, but a fuel proof one would be better, like pro seal, PRC....

did piper even use any????(I never reused piper boot cowls-direct to dumpster.. just made my own or used Atlee's )

I've done 2 and didn't use any sealer on either and they've both held up fine.