I did my first tank not 2 weeks ago. just with spray cans. when i got to laying down the clear coat it started to get cold outside and i tried 3 times to spray and it kept coming out cloudy. Really milky. It was bizzare as. I found out that it has to be slightly warm conditions for it to turn out right. I waited for a sunny day and left the cans in the sun for half hour and came out and sprayed and it looked awesome after that.
So weather can be a big factor.