Well, if anyone's interested, I did talk to the camp manager, as we wanted to give feedback about the situation. He was so nice and said this is a situation they've been dealing with for years and they find it extremely frustrating as well.
He told me no matter what they do, people will start "tailgating" (his words) by 9am in hopes of being first to check in. People will even go to the town on the other side of the lake, rent a boat, and get in via dock to skip the car line.
They do open the front gate, as camp behicles have to get in and out and they cannot have the long line on the highway. They have even (and I don't like this part, but what can I do) started processing cars (forms signed, temps checked, etc) before 2pm outside the gates to get things moving along) However, he said no car is allowed in the inner gate until 2pm. Kids do get out of the cars, and wait by the cabin, but he said the cabins remain locked until 2pm. He said that we likely arrived about 10 minutes after the inner gates opened, all the waiting, processed cars had pulled forward, and we were just waiting behind the dozen or so cars that still needed to be processed. By the time we got to the cabin 15 mintutes later, the kids had all rushed in.
They have tried different systems. Yes, I think that assigning bunks would be best. The manager said they had many parent complaints with that system (can't be on top bunk, has to be beside friend, etc), so they went back to the first come first pick.
What he said he would consider doing was being more explicit in the information packet about the "tradition" of arriving hours early. Ie state that bunks are assigned first come first serve and that anyone arriving hours early will have to wait and will not be assured their first choice bunk. And that the camp recommends that campers would do not care about their choice of bunk arrive 30 minutes to an hour after the start of check-in time.
Honestly, given this choice, there is no way we would have sat outside for 4 hours (with a toddler in the car as well!). But, I do like his thought about at least making the real situation more clear.