I used to use roofing tar mixed with gasoline (grew up in the rust belt), the gasoline would evaporate and I applied it with a suction sand blaster...worked good, last a life time. The cars would rot around the tar...Tim

1941 Taylorcraft
1968 Charger
1994 Wrangler
1998 Wrangler
2008 Kia Rio
2017 Jetta

I didn't do 4 years and 9 months of Graduate School to be called Mister!