Yes, I was the one :-) I install a 8 Onz Dubro fuel tank. I am pretty sure that maybe you can install a biguer one. You have to find a diferent brand because the Dubro 10 Onz was to wide and does not fit.
Here is the tread about this and other advises:
http://www.rcuniverse.com/showthread...78&forumid=162
I also recomend you to reinforce the front mounting block on the fuselage were the wing is atachet with one wood dowel.
I was checking my airplane and there is a play on the wing in that part.............I found that part/wood that have a hole in the fuselage has a crack near the wall of the fuselage, so I have to reinforce that part with epoxy.
Maybe that part crack because a hard landing.
Isaacc