Rich:
I use cup hooks. You can get them down to about 3/8" across. I make the holes, screw in the hooks, verify that everything fits, then I unscrew the hooks, put a drop of 5-minute epoxy on each screw, and screw them back in. I have had exactly zero problems with tank mounting when I do this.
If you want to be really anal retentive about getting an Absolutely Perfect Tank Mounting, then get some thin aluminum (1/32" is best). Cut a piece out that's about 3/4" wider and longer than the tank. Bend it into a channel that cradles the top and bottom of the tank and cut slots into the front and back of the sheet. Then screw that channel into the fuselage with about 1/4" of kick-out in the back and hold the tank on with cable ties. You'll be able to exactly adjust the height of the tank with ease.
For a Ringmaster, I use cup hooks...