If you have wide enough temperature variations, you may still have some expansion/contraction problems. One member of our modular club used to constantly complain about people leaving small gaps between the ends of the rails from one module to the next in our modular setups. When he was put in charge of one set up at a mall, he insisted that the rail joiner tracks be cut exactly to fit between the modules without play. It worked fine on the Friday night set up. The next morning as the sun came up and began warming rails through the mall's skylights, the rails started warping when they had no room to expand! We ended up removing joiner tracks and cutting them to allow a 1/8 inch gap at each end of every module. If you have drops soldered to every section of rail, a small gap between sections of track won't hurt your electrical continuity at all, but will allow for expansion of the rails. That is one reason that I always reccomend for people to solder drops to the rails and not solder rail joiners or try to use rail joiners for electrical connections.