As stated above a dual tank system is fine. Us heli guys use it often. The 1st tank that the motor draws fuel from stays full until the aft tank is fully depleated. Because of this I would advise you use the bigger tank in front of the CG and the smaller one aft. Additionally, make sure the main tank for the motor is the one in front of the cg. If you did it reversed the motor would drain the front tank first, causing a rearward CG change (not good).

Good Luck!

Here is a pic of the setup on my heli (Courtesy of DJ Vegh's site):

Phil (Mesa, AZ)