Humidity and temps belong together,a)... if you can rise the temps you can lower the rh.....
so look for a warmer place to grow.......get a little heater with tempcontrol
.b) give airflow..... open up the tent if lights are on.....get an intake/ exhaust fan ,get more fans......etc. and 60 are not too bad your plant has enough space inbetween , so i wont be so concerned, as long as your try to oepn the tent daily to dehumidify