Some temp. and humidity questions

I have a question about temps. Im growing in Ca with a tent, but the tent is outdoors (couldn't make the necessary modifications to keep it indoors or in the garage) under a RV type parking. Temps range from 72-82 with the lights on. (I run my 12/12 at night to cut down on the power bill and thats the only time im home to do my checks since they're in the light) Temps during the day in the tent range from 59-70 in the dark depending on how warm it is. Is this too cold for mj to grow? Also the humidity hovers around 48-60% but ive seen them climb to as high as 90% (when it gets way up is usually after the light have been running all night without my portable ac unit on so I just turn it on for about 20 min and it goes right down) Are these numbers acceptable to grow decent mj? My plants are exactly day 18 from 12/12 and are showing pretty good signs of flowering. They seem to be pretty healthy except for some lower leaves on a few plants drooping and dying. Im also worried that when it gets even colder outside they wont withstand the temp drops. I can keep it pretty stable during the time im home with lights on, but during the day it just kinda does its own thing. Maybe im too worried

Furthermore, I should be harvesting by estimate this first grow for me around the end of Nov (11/23 is 50 days flowering exactly) and I will be rotating another crop so I might be a little colder. Any suggestions would be appreciated. I was thinking about maybe adding another light to keep the temps up a little.