Hello and welcome!
Please add the make,model and year of your camper to your signature. This helps us to better help you.
You say that you replaced the battery and had some blown fuses. That usually happens when the battery is hooked up backwards. With the colors of the battery cables it is easy to do and is a somewhat common occurrence. That said the 12 volt system has nothing to do with the fire place.
Have you checked the breakers - turn off then back on? Sometimes a tripped breaker is hard to see. Also is your camper 30 amp or 50 amp? If 50 amp are you plugged in at home and is it wired correctly? One other thing is the fireplace in a slide? If so check the junction box under the slide.