Definitely easier to spray the back before the tank is setup..did both my 75g&20g after they were setup..thought it would be difficult but not so much..I used a 6" sponge roller with valspar black primer(dries fast)the black gives added depth to the tank..4 applications 15min apart with a fan blowing behind the tank to help speed up the process..you also might want to use a small foam brush for touch ups around the rim...really impressed with the results,with the added illusion of depth&how it makes everything pop out I think you'd be happy also..I'll post a pic a little later..