I use up to four portable space heaters in this RV but I have a warning.
In some cases, when a heater was plugged into one of the OEM outlets, I noticed the aroma of hot wires. Now this is not something I care to smell, for one thing, I know that if the wire gets hot enough. Bad things happen. (I finally replaced the outlet, wires did nto look that bad but there was clearly heat damage)
To resolve that I installed two 15/20 amp outlets, These are standard household outlets with the "T" shaped neutral slot, They are connected, each to a circuit breaker that feeds only that outlet using 12 gauge wire which on the outlet end is bent around a screw and properly tightened.
The 3rd heater runs on the Washer/Dryer outlet in the Washer/Dryer (optional not selected) cabinet, #4 does not often see the light of day. but if it does I keep it on LOW.