Condensation occurs when a surface is cooler than the dewpoint of the air around it. You can try to keep the surfaces of the inside of a boat from getting cold by insulating, but if you don't add heat, the surfaces will eventually cool down anyway. Insulation
slows heat transfer; insulation
does not stop heat transfer. Many boat owners, like me for instance, can show you mildewy boat insulation that gets soggy from condensation.
What you want to do is lower the dewpoint inside your boat so its is less than the outside temperature (water or air). You lower the dewpoint by lowering the relative humidity (RH). You lower the RH by either raising the air temperature or extracting water vapor out of the air (usually through condensation and proper collection and removal
of the condensate through a drain - this is how dehumidifiers work), or both.
So you can insulate to retain heat, but you will have to add heat. With a boat that small, you might be able to get by with a small electric heater, powered by PV, and skip the insulation process. If you have acces to shore power
, you could use a dehumidifier.
my condensation problem by covering my boat with a tarp and an air space between the tarp and the deck, which cuts down on convective and radiant heat loss at night, and keeping the companionway
and a hatch
open, which allows daytime air, with its low RH and high temperature, to heat and dry the boat out naturally.
One last thing: before you try to insulate or heat your boat or do anything to get rid of mildew, you must first make sure there are no leaks into your cabin and no standing water (like in the bilge). Otherwise all you efforts will be for naught.