Condensation occurs when warm moisture laden air comes into contact with a colder surface, reducing the relative humidity to the point that it condenses into liquid water.
There are two approaches to dealing with condensation. One approach is eliminating or reducing the temperature differential between the surface and the surrounding air. The second approach is to reduce the humidity in the air. A combination of both approaches is generally the most practical.
Starting with reducing the surface to air temperature. If you can fix some insulating material onto the areas that are getting condensation you will either reduce or eliminate the condensation.
The second thing to look at is the air humidity in your motor-home or boat. Most of it is likely to be coming from the occupants. People release a huge amount of moisture into the air just from breathing. For this reason ventilation is king. It may seem counter intuitive, but keeping everything shut up to keep the warmth in, will often make things feel colder, because of the high humidity levels. You should have vents in your boat/motor-home. Make sure that they are open at all times. If they already are open, then try to keep a window/hatch cracked, if possible.
It is also worth evaluating any heating system you may have. If it is run on gas and is not flued externally, it will be introducing huge amounts of moisture into your accommodation, as will cooking and showering.
Humidity is relative to temperature. What that means is the higher the air temperature is, the more water it will hold in gaseous form. When the temperature reduces, it can’t hold as much water in gaseous form and must release some of it in liquid form, usually by condensing onto a cooler surface.