that moisture is condensation from wet/sweaty clothes, your breathing, showers or cooking. In combination with being cold outside, the moisture gathers on the cold skylights. Hard to stop, but controllable.
You can minimize moisture inside, as already mentioned - keep wet or damp stuff outside, leave a window cracked for ventilation while sleeping, minimize cooking inside, you can put insulation on the inside of the skylights - which might help but should be monitored for signs of absorbed moisture, and keep the inside temps cool - minimize the temperature difference. We practice all of these things on every trip, except the skylight stuff as we don't have any.
You could try the silver bubble wrap insulation that can be purchased at any big box store. It might help, not heavy and won't absorb moisture.
2000 Cherokee 29BH with 6V batteries, LED lights & 400 watts of solar power, flipped axles and raised. 2007 Tundra 5.7L DC-LB with lots of mods. C-co, 8/158th AVN Maint.