looks like a small van or SUV would do
I watched some videos on youtube.com, and it appears that a RIB could easily fit in a van after being partially deflated. In fact, it looks like a small van or SUV would do, providing that the engine will fit in the hatch.
Allowing that the engine can be tilted approximately 45 degrees, I think an opening of 2 1/2 to 3 feet high would do.
If you would like to see the videos, go to youtube.com and search for "stryker inflatable" and look for the dude standing in a small store room narrating the video.
He also uses a nifty self-contained inflator about the size of a small vacuum that would be nice to have.