Used Proseal tank sealant. Did not know any better. Hopefully I shall be back on the ground in one piece before the Proseal fails and allows smoke and flames into the cockpit.
Related topic. Firewall insulation on the engine side. Look into that before you hang the engine. First time I flew with short pants, I was surprised how hot the footwells become.
RV-14A Flying Jul 2020, thanks to all