Even the undiluted chlorine will last quite a while if you keep sunlight away from it and try to keep the temperature down. The half-life of 10% chlorine at 77F is 220 days while at 140F it's 3.5 days. If there are contaminants in the chlorine, then it can degrade faster. A 50/50 diluted mixture that started with 6% will be 3% and the half-life even at 100F is theoretically more than 1 year so you should do just fine so long as you keep out exposure to sunlight (you most definitely should cover your reservoir to keep out the sun).

You can get some outgassing of chlorine and even if this was relatively low so that the strength didn't decrease much, chlorine gas is poisoness and a very serious oxidant that will wreck havoc with your pool equipment, so I would cover your pump with only the smallest hole necessary for bringing in air (if needed) to prevent a vacuum.

I doubt that the UV from sunlight will penetrate white piping so I think you are fine there as well.

Richard