Fire hazard is always an overriding concern in an RV. The use of electric heaters is very common in the RV community and problems caused by them are pretty rare, largely due to improvements in such heaters and the education of users. Without question, the safest electric heat for an RV is to have heat strips installed in your air conditioners but that can be expensive if yours did not come with them. Space heaters can be used safely, with proper precautions.
The safest type of portable electric heater is the oil filled radiator. The oil diffuses the heat across the entire surface so nothing gets hot enough to present a fire hazard. But they are the largest and most bulky of commonly found heaters and they depend upon convection for heat distribution.
Ceramic heaters operate at lower internal temperatures than heaters that use wire grids. As such, they present less fire hazard than conventional heaters if tipped or if something accidentally comes in contact with the heater. All portable heaters should be epquiped with an over temperature switch and some also have a tip-over switch for additional safety. As a heat source with a small footprint, the ceramic heater is your best choice. Most also have a fan that helps to distribute the heat.
The glowing, infrared, radiant heaters provide a warm, fireplace-like glow and are inexpensive, but they are also the most dangerous of these appliances. If they contact flammable material they will cause a fire. The quartz heater is really one of the wire-wound radiant heaters with the element inside a quartz envelope. It is only one step above the old fashioned kind and I would not use any radiant heaters in an RV
Electric space heaters typically have a rating of 1500 watts, and most also have a low setting of 750 watts with a few having three settings. But those settings are based on the power used by the heater and do not tell you how much heat each makes for the power consumed. That is rated in BTUs and only one or two manufacturers give that information. When you shop, if the packages do list the BTUs produced, you want the one that has the highest output for the 1500/750 watts that is used. The two designs that supply the most heat for the watts used are the oil filled and the ceramic.
Any electric heater will be drawing nearly the maximum rated load of a duplex outlet, probably for an extended period of time, and RV sockets are not usually of the highest quality. A heater should always be the only thing plugged into an outlet leaving the other half vacant. A slight warming of the plug while the heater is operating is normal, but if you notice any heating of the outlet itself or if the plug gets hot enough to deform the plastic around the prongs you have a wiring problem that must be addressed. If you replace an outlet, do not purchase the lowest priced one available as they vary in quality, as well as price. Buy one in the mid to upper price range and from a known manufacturer.
The same rules apply to your shore power plug. Safe use of the full capacity of your shore power is dependant upon all equipment being in good condition, which isn’t always true. You should examine the plug to be sure that it doesn’t show signs of damage. If the outlet is not in good condition it isn’t safe to use, especially if you are using heaters or air conditioners. It should not show signs of having overheated, cracked, or of weathering. You can improve the electric connections by applying a small amount of dielectric grease, available from a home supply store, to each pin of your power plug. A bad outlet can damage your RV’s power plug, or worse.
A 30 amp circuit will be running at close to maximum capacity with two 1500 watt heaters. Add the other miscellaneous loads like lights and TV and you're probably at or exceeding that limit. It is wiser to use only one heater, or use two in different locations, but with each set to the low setting. If you have a 50A power cord you can probably use two heaters at the same time safely. If you do, make sure that each one is on a different electric circuit. With 50A service, it is a good idea to install a separate circuit for each heater that you use. Install a 15A circuit breaker into the distribution box for each using wire of 12/2 design and install a single socket outlet for dedicated use on each. These dedicated outlets are usually orange in color to indicate that they are on a separate circuit.
Never use an electric space heater with an extension cord. Even a very heavy cord creates problems because each electric plug uses friction contacts that are a source of heat when current passes through them. Each time you add another plug you create another danger point. Feel the cord of the heater and the outlet frequently and if they are more than warm to the touch, do not use them. Place the heater on a hard surface where it will not get tipped over or the air path blocked. And only purchase products that have the U/L label. And always read and follow the directions that come with the heater. By following basic safety rules electric heating can be done safely.