Whichever tank fits 'Perfect'ly... Sorry, I cannot be of help, but I just had to.

I just got a cox 010, always wanted one as a kid, found plans now got convinced to build an airplane for our club demos.  

I have no intention of building a stunt tank that small, which perfect tank will work?

Here is a tank I built for the Cox .010.  Externally, it is 12mm (h), 16mm (w), and 30mm (l), or something less than 5.7cc - less for interior dimensions and tubing, so the whole thing is less than 0.2 oz.  (Based on 30cc - 1 oz of fuel, approximately).  This give enough of a run to get four of these things started, takeoff and complete 10 laps.  This is a square tank, set up as a uni-flo, with the pick-up and vent on the bottom outside portion of the tank.  So, depending on what you want to do, a Perfect tank, around .2 oz will work for a run of up to 2 minutes or maybe less less.

Keith

I would go for a small balloon tank.  I have had good luck with them.  The only problem is you need to replace the balloon once in a while.  I think it is the oil that eats them up with time.  If you are not going to fly the aircraft for a length of time I would remove the balloon and discard it.  It's been my experience that they turn to mush with time.