Winter in North America invariably breeds the perennial question: What space heater is best for using in my RV? It's as bad as a "Ford v Chevy" question in terms of what answers you'll get.
First, why a space heater? Many RVers complain that their factory equipped RV gas furnace is a huge LP sucker. It's true, because of the nature of RV furnaces, they don't put all their energy into your RV--a considerable amount is blasted outside. That's to keep the firebox (and it's associated combustion byproducts) isolated from your living quarters. Heat is produced in the firebox, which liberates nasties like carbon monoxide into the outside air, transferring the hat without the nasties, into your house.
Enter the space heater. Most, if not all (depending on the heater design) of the heat produced by the space heater is given off inside your living quarters, hence far less cost to heat than using the furnace. A space heater can also keep you warmer for less, because you determine whether the heat goes in your rig (say keeping the bedroom closed off and unheated by day) rather than blasting heat into every section of the rig, used or not. Now let's break down space heaters based on their fuel types.
Gas space heaters: Generally fired by LP from your rig's own factory equipped LP containers, although some use disposable or portable LP containers. A gas space heater is basically the only way to space heat when boondocking away from shore power, as firing up a generator to give electricity to an electric space heater just blows any efficiencies out the window.
Catalytic space heaters don't have an open flame for heat, but rather use a special 'catalyst bed' to produce a radiant heat. A radiant heater produces heat quickly for any object or person directly in its path. Great for use even outdoors, or in a poorly insulated RV. 'Cat' heaters generally don't require any electricity to operate, so they're a favorite among boondockers. To heat a large area of an RV it take a LONG time, as the heat first has to be absorbed by nearby objects, then given off to a wider area. Most are non-vented, meaning the take their oxygen from the room to burn.
'Blue flame' style heaters are as they sound, a flame type heater. Typically the flame is shielded behind glass or a metal grill. Flame type heaters will warm a large area of your RV, but they take a little longer for the heat to penetrate a nearby body than does a radiant style cat heater. A few flame type heaters are made to be vented outside the rig, but they're quite rare among RVers. Look for an oxygen sensor when shopping for a non-vented flame heater. The sensor will shut down the heater in case the oxygen level in the rig begins to drop to a danger point. Some RVers have complained about watery, burning eyes when using a flame type heater.
Be careful to read the instructions with your non-vented heater. Most require having outside air available for safety. That translates to leaving a window or roof vent open to allow a certain number of square inches of outside air inside. Don't ever bring a portable (refillable) LP container into your rig to fire your space heater; and if plumbing in a line to fire your heater from the rig's LP supply, don't use a standard air-line "quick disconnect," but spring for the extra few bucks it costs for a gas-rated disconnect.
Electric Space Heaters: If your RVing keeps you close to shore power utilities, and especially if your electricity is included in your rent, electric space heaters are particularly attractive. Like gas space heaters, there are different types of electric ones.
'Radiant' space heaters very often rely on halogen technology, a tungsten metal filament inside a quartz envelope. These produce lots of radiant heat quickly, like a gas-fired cat heater. Again, it's great heat if you're sitting in front of the heater, but it can take a long time to heat up a large area.
'Convection' style heaters are just about anything else in terms of an electric space heater. Wire coils either provide direct heat, or indirectly through some medium like an oil-filled case. Some have fans to spread the heat into the room faster, others do not. In terms of efficiency, that is, how much heat your get for how much electricity you put into the beast, there is almost no negligible difference.
Much of the difference between electric space heaters is a matter of safety. Oil filled heaters have a fairly low surface temperature, hence if they fall over, probably won't do much damage. However, the oil-filled heaters take a long time to produce heat, and are better if you'll have them on for hours at a time. Other heaters that produce heat in a hurry often have 'tip switches,' that shut the heater down if they tip over.
Still, take safety seriously when using electric heaters. Don't run they on an extension cord if at all possible. Never route their cords under carpeting. Keep them away from kids and pets. It's best never to leave any portable electric space heater running when you're not around. The same is true for portable gas heaters. Those that mount to the wall may be safer, as they're less likely to get knocked over by Bowser or an unexpected earthquake.