it's not too wide. With the help of my father in law, I built an 8x6 that we also use to haul dirt when we were re-landscaping the back yard. 4 dirtbikes fit in there without cramming them in, and isn't too wide for any lanes anywhere. can't say it's NEVER a pain in the ass, but I've taken it as far away as central oregon from the bay area, works great.
you might check out sears, I bought a small setup from them 7 years ago and basically put a rail on it, you might fit 3 rails on em, but it would require some work but alot cheaper than a custom made one.