Hey Robert.
I've never had an issue with balance of any of my Roscoe's (and I've owned multiple basses of all body types). I use a Comfort Strap and the bass just sits where I move it (the strap sticks very well to my shoulder).
On the Gecko however, since mine has the metal rods in the neck, it is a bit neck heavy. Still, using the Comfort Strap, it pretty much stays where I put it. Sitting, without using the strap, it does have a bit of a balance issue.
If you decide to go with building a Gecko I'd get the optional graphite reinforced neck (in lieu of the STD metal rods). I suspect that it balances much better.
My Gecko neck is a medium and it plays wonderful. I've had it for about 17 years and the neck has never moved at all. Super action too.