Certainly! Many of our customers use additional heaters in their cabin spaces to protect water lines, heads, etc.
Realize that the volume of your cabin is much greater than the engine spaces of the boat, so size your heater(s) accordingly. If you are using multiple Xtreme Heaters, be sure that you are not running too much amperage through a single electrical circuit on the boat. It is always a good idea to plug your heaters into outlets on separate circuit breakers to prevent overloading a single circuit.