well, here are pictures of my almost completed extra. All I have to do is get one of the elevator servos reversed using a friends programmer and then mount the battery packs to balance. Preliminary balance seems to be dead on, so will probably mount battery packs right near the CG. I did not have to add any weight to tail or nose. Haven't had a chance to weigh it yet for total all up weight, but it does have a sullivan skywriter smoke system that probably adds a pound or so. Depending on final weight and the way if flies, I may opt for the carbon fiber wingtube.

Oh, forgot to post the details:

DA-50 with slimline smoke muffler
Hitec 5945MG servos on ailerons and elevators
Hitec 5955TG on rudder with 3 inch double arm from airwild
hitec 325's on choke and throttle
two redundant NoBs Batteries on receiver (6 volt 1500mAh packs), each with own switch
one NoBs battery pack on ignition (4.8V 1500mAh pack)
sullivan skywriter with thunder power LiPo pack for power (7.4V 700mAh pack)
Airwild twisted servo extensions
JR heavy duty charge switches x3
NX pro 22x8 prop
Dave Brown aluminum spinner
Dubro wheels
two 20 ounce dubro tanks (one for smoke)

Last touches that I am waiting for are the pilot and DA fuel filler. Both are on order. The pilot is the Aircraft International foam pilot.

As you notice from my battery pack choice, I wanted to keep weight to a minimum, so I chose some fairly small packs. I usually don't fly more than 3-5 flights in any given day, so those packs should be plenty. The 6 volt packs each weigh 5.6 ounces and the 4.8V pack weighs 4.7 ounces. I think you Li-Ion guys probably have around the same weight (or more) using your larger capacity packs and regulators.
The little Li-Po I used for my smoke system weighs less than an ounce, and I don't need any voltage regulation for it since the skywriter uses voltages between 4 and 12 volts. THerefore, I am hoping the overall weight of my system isn't too bad, even though I have the smoke system installed.