CM's can be a big pain when going through the toll plaza. But just make sure you stay in your lane (resort lane).
There's a letter for each toll booth (W-E-L-C-O-M-E). During exceptionally busy times, E will be open, the right side is for Disney busses only (all the time). The right side of M is "cast only". Since every one just flashes their ID and gets waved right on through, it's a little tough in the morning to get through. Left side of M and right side of O are both considered "resort only". This is for any one going into the resort area and not the main parking. In a big rig, stay on the left side of M. Usually by 10-11am it quiets down and is much easier to get through with merging. And check in is at 3pm.
Although it sounds like a pain to merge to the right. Don't be afraid of cutting off a CM (you're probably in something much larger than them), just becareful of the busses. They do have to come to a complete stop at the toll plaza so that would give you the opprotunity to get in.
If you come in from the north end of the Magic Kingdom on reams rd (so you can make a left into the campgrounds), you have to stop at a stop sign and wait for the traffic to clear coming from the toll plaza. So it's even more of a pain to get across sometimes. But some bus drivers are usually nice and will slow down some to allow a big rig or another bus go through the stop sign.
If you come from the North end of the property, you can also make a right onto Vista Way, which then you have to make a right into the Fort. Which for some big rigs can be a pain.
If you do wind up arriving very early, you're best bet it to park in the overflow lot. Which is the parking lot on the left. It'll say "pioneer hall" and "kennel" on the sign. This is a regular turn in, so you can come in from either direction. This is were you'll park your rig till your site is ready, and just across the way is the bus shelter for the theme park busses.
The red line is coming in Vista from 535, the purple line is coming in from reams road, the yellow line is coming in western way but up through World Drive main entrance.