Bob,
I’m so sorry that I missed this post until now. I’m out of town right now on vacation, so I’m a little distracted.
Anyway, thanks for asking about a pickup for your bass. The Coratado MkII kit sounds like it might be a good fit for you. You might consider modifying it by replacing C1 and C2 with bigger caps…try 12 or 15nF, to allow better low frequency response…it will pick up low harmonics better. I wouldn’t suggest getting much larger than 22nF or so or it will start sounding too big and muddy in the lower frequencies.
Also, you might want to try to add another piezo sensor in parallel to the first one (just make sure they use both the same wiring configuration or you’ll get phase issues). That way you can add one to somewhere around each side of the bridge to get a better frequency pickup range.
In my experience, this should work pretty well for your bass, as long as there aren’t a lot of things rattling around inside of it. Good luck!
-Brach