Hi Thomas,
They are very similar in their care to the meru's. They like cool temps at night (40-60F) and daytime temps in the 70s. They are very sensitive to supplements and/or crickets from cricket farms. Something in the cricket feed causes edema in the johnstoni. Incubate eggs at 70f for 100 days.
My indoor johnstoni have a heat light on in the AM only, and seem to enjoy basking for a few hours.
Let me know if you have anymore questions. There is a FB group on African Chameleons that also has many johnstoni keepers too.
Enjoy,
Tylene