I remember that being a tough job. I used laquer thinner, MEK, a scraper, and scotchbright. Given that the oil pan is cast (and has indentations and other irregularities) I wasn't able to get every speck of paint off of it, but I did remove the vast majority of it. Probably 95% or so.
No problems in the 3 or 4 seasons I've had my hotstrip.