Radio Shack's RG-8/U is the same as any companies' RG-8/U (solid center conductor and 97% braided shield), just twice as expensive. I am still using some of the several hundred feet I bought in the late 70's (sold at $.21/foot - cut at the store from giant spools) Be that as it may, coaxial cable use as a transmission line is very lossy and running long lengths of coax attenuates TX significantly particularly on higher frequencies (the higher the frequency, the more attenuation). I would go with 600 ohm open-ladder line (with a balun) as a transmission line, the balance between the two conductors leads to less loss of RF signal but you risk electrifying trespassing neighborhood kids, but hey, if you are going to make an omelet, you gonna have to break a few eggs, Right?
Joe