When DD was little, we purchased an Aero Bed toddler size "sleepaway" bed. It was about $100, and such a GREAT purchase! It comes with a pump and matress pad, and is a bit smaller than a twin bed. The sides are raised so the child won't roll out of bed. It has its own carrying case, and we've both taken it as a carry on on the airplane, and checked it through with no problem. We used it at the BWV as well as many other trips, as my kids won't sleep together. I highly recommend looking into this! She used it for years, from about age 2 until 5 or 6 even.
For our upcoming trip (in the planning stages) to BWV, we're probably driving and definitely taking a twin aerobed. My kids won't share the sofa sleeper, and I think there's room next to the master bed for her aerobed.