Unfortunately long distance endurance racing is a 'niche' activity in SCCA. There are two major long distance races in the East - The Devil in the Dark 12 Hour at NJMP and The Charge of the Headlight Brigade 13 Hour at VIR - which use the same basic rules and attract many of the same competitors. The Longest Day 12/24 Hour at Nelson Ledges was contested for many years but has unfortunately been inactive for the last couple of years due to of lack of support. Two races aren't a 'series' but they are a healthy outlet for endurance racers and one worth traveling to compete. The last two overall winners of The Devil in the Dark have come from Canada and Louisana.
As I stated on another forum, we will make a place in the The Devil in the Dark for Chumpcars which can meet SCCA IT safety specs. Generally, I understand that Chumpcar is not that far off from SCCA in the safety area.
Hope to see ya at The Devil