We took the Malaspina from Skagway to Haines in July 2013. We had no reservation until the day we planned to leave and had no trouble getting a reservation for that afternoon at 3:00. Our truck and trailer were measured in the parking lot by the ferry dock workers at exactly 40 ft. Most of the vehicles loading at Skagway were RVs--motorhomes, 5th wheels, travel trailers, and pickup campers, a couple of commercial trucks including a semi, and a few cars and SUVs. Despite the number, the ferry was not completely full that afternoon.
Everyone boarded through the side at Skagway and unloaded through the same side at Haines. We were one of the last to load and drove up the ramp, turned left and parked in the middle lane facing aft. When we unloaded, we were directed to loop around the central bulkhead and drive toward the bow, make a right, and headed out the door. We had no problem getting on or off, made the turns with no trouble, and, as others have said, everything was handled very professionally.
We have used the ferries twice now--in 2000 from Juneau to Skagway to Sitka and this year from Skagway to Haines. If we go back to Alaska again, we will likely take the ferry at least one way from Bellingham and maybe both ways. It really is a great way to see Alaska, especially in the Inside Passage.