The level of condensation that I experienced is not going to work. Not only did I get droplets on the ceiling, but also my gear was moist with condensation. That is no good for long term travel.
When trying to reduce condensation in a sailboat in a previous project, the answer was insulation, ventilation and heat. I am not going to heat my bicycle camper, so my options are ventilation and insulation.
I will continue experimenting with cold weather overnights to see if additional ventilation will reduce condensation, but I suspect that a foam cap is the way to go.