I'm a regular at NHMS for the June race. I'd suggest a stay from Thurs. thru Monday as "bugging out" on Sunday might be impossible!
When staying on the track property, people are jammed in pretty tight. Between awnings, parked vehicles within the roadway, turning radius, the ability to pull up stakes and leave can be nil.
Unless you can manage an end row parking position, I'd plan for a longer stay.
I can't speak to off track parking because I've always stayed on site. However, there are quite a few off site locations available along the way to the track. Problem here is the walking distance to the track and the load you have to carry (ie. cooler,seat cushions etc.)
Any other questions/concerns ask away and I'll try to help.
1997 F53 Adventurer 37rw
IAFF L-792 (Retired)