Unless you are running 2 heaters or other high wattage devices, there is no need to run a seperate cord in.
I lean towards a ceramic heater with tip over protection (it shuts off if tipped). The oil based units will put out the same heat...once they heat up. The ceramic put out heat almost instantantly. Usually we use it to take the chill off in the morning and quick supply of heat helps.
Side note: I suggest you poke your head under and inside the storage areas of your RV. Unless it's something special, no way is it sealed in such a way that it will keep mice and bugs out.
There should be a duct or open space between the breaker panel and the cord door to get the 30amp cord to the breaker panel. If you really want a seperate cord, you should be able to follow that path without creating a new opening.