This is what he's talking about if I understand him. There is a tubing and power umbilical that connects the two components. You can get different indoor units to suit different mounting arrangements.
Probably would not be my first choice based on what you appear to be doing. These are not cheap, plus, the colder it gets outside, the lower the heating capacity. Can you do it with these? Probably, but might not meet your budget. On the plus side, they are very efficient when the weather is moderately cold.
Several folks have recommended ventilation to prevent condensation. This is the best way to reduce interior humidity - better than your dehumidifier when it's cold outside.
The right way to go at this is to calculate your required heat load and size your heating units to meet the load. You have to include heating any vent air in your load calc, if you choose to use ventilation.
Like several others, I'm not sure how much hull insulation you can practically accomplish. I would insulate the interior using products that won't contribute to rapid flame spread or smoke development. I would heat and vent the cabin and circulate cabin air through the bilge and exhaust or relieve from the bilge to outside. In other words, you bring fresh air in through a heater that blows in the cabin. Install a bilge blower that pulls cabin air in and blows into the bilge. Then, verify that you have a path for the bilge air to exit.
Again, insulate the interior to the extent you can, then get enough heat to meet the conditions you want to maintain. Decide what energy source you want to use. If this has limitations, you may have to increase your insulation to allow you to meet your desired interior conditions. This iterative process is best done on paper. Working it out through trial and error can get expensive and frustrating.
If you do this correctly, you will have an uncomfortably dry boat. But, if you don't want condensation, that's going to be part of it. Maybe you can stand low humidity better than I can. When it gets under 50% rh, I start getting chapped lips and dry skin. Of course, where I live, you need gills to breath the air...
If you tent the boat, use care when using diesel or other combustion heating.
It's not rocket science, but it works better when it's appropriately designed.