I once built a 4 x 12 foot track that was very portable. It was designed as three 4 x 4 foot modules, each of which I could lift and carry by myself. Each module had a handle fastened to the underside, which helped a lot. I took that track to many slot shows, setting it up and taking it down by myself in about a half hour. I still have that track. It is set up in my basement. It has needed some maintenance over the years, but otherwise has been very successful.
I also once was able to manhandle a 4 x 8 track onto a roof rack on my car for transport to and from a slot show. At the limit of what I could life and carry myself, but I was young and stupid then.
You might be able to build a portable 6 x 18 track in three 6 x 6 modules, or perhaps in four modules. Very difficult for one person to handle, but workable with two people.
The trick will be assembling the modules with smooth track joints. What worked for my 4 x 12 track was bridging the module joints with removable sections of track. That made the alignment of the modules much less critical. It only took a few minutes to line up and screw down the bridge sections, and their transitions were square and level.
Ed Bianchi