Moisture can appear on the inside of your skylight frame
Water can form on the inside of any aluminum metal when it is cold outside and warm inside. This moisture is called condensation. This can form even if you have a thermal break in the frame that prevents the inside metal from touching the outside metal. (reducing conduction) A good solution is to get rid of the aluminum and replace it with non-conducting materials.
There are good quality skylights, such as Velux, that are designed without the use of metal on the inside support structure. This prevents condensation from occurring on the frame.