We replaced ours back in 2013. I went with the assembly replacement as I was concerned about fashioning a hose connection at the hub of the spool that would not chafe and lead to early failure of the replacement. They come in 35' and 50' lengths, now. And yes, we went with the ½". I don't feel that the flow rates of motorhome plumbing systems would require the ⅝" hose. Also, it may be that the ⅝" hose would limit you to the 35' length in order to fit on the spool.
When we set up for weeks at a time, I slip one or two black styrofoam pipe insulation pieces over the hose to limit the UV damage from the sun. I also try to "toss" as much of it as I can under the coach or otherwise route it to keep it out of the sun as much as I reasonably can, for the same reason. It has held up magnificently.