I don't know for certain but they allow buses and commercial people hauling vehicles to do the Holiday Lights Fair drive so I can't imagine they would turn you folks away because you are a truck pulling a trailer. You will enter off of U.S. Rt. 51 on the west side of the fairgrounds. The drive is a little over 3 miles and winds throughout the fairgrounds. There are even lights mounted over water of the ponds that are part of the fairgrounds. They usually have lights all over the back side of the main grandstands for the mile track and most all the grounds buildings are lit up with Christmas lights. The price has recently gone up. It's now $10, not long ago it was just $7. Still worth it. I think they've advertised in the past that there are over 1,000,000 lights. http://www.duquointourism.org/index.php?page=lights

Can't help you with the pit pass seating question. However, I don't remember there being seating for people in the pits that is segregated from the GA seating. I'm sure someone here is familiar with how that works.