If you knew how poor the workmanship can be when they wire outlets at the factories, you'd definitely want a dedicated outlet when running heaters for extended periods.
Cords on 1500 watt/15 amp portable heaters are often only 16 gauge wire (and meet UL). Do not coil the cords up and/or hide them under carpets or they can overheat. Follow the heater's clearance requirements.
Low voltage is very common in the summertime from many RV-ers in a CG running AC units and how low the voltage gets depends on a few factors, including how old the CG is and how it was wired. Low voltage won't hurt an electric heater but it will lead to damage in AC units.
Note that the heat output of an electric (resistive) heater varies as the square of the voltage as per Ohms Law, based on a nominal line voltage of 120 volts (the industry standard). Say the voltage got down to 104 volts, the point at which an EMS will cut you off, the heater output would be down to 104/120 x 104/120 = 75% of it's rating. If it seems like you aren't as warm as you'd expect, it could be the voltage is getting rather low. Plugging in or turning on another heater may only cause each heater put out even less heat (from more voltage drop).
The condition of a pedestal can also be a factor in voltage drop. 50 amp pedestals are generally in much better condition than 30 amps though. A 50 amp RV should not have a problem with a couple of plug-in portable electric heaters as far as the 50 amp service goes. Your AC units probably draw as much current and maybe more. There can also be some voltage drop on the wiring from your panel inside to a receptacle. Having a permanent voltmeter mounted inside is always a good idea so you can keep tabs on voltage at any time. There are some good plug-in LED ones or install a hard-wired type. An EMS is a good thing to have and will automatically protect you against low voltage (and a few other anomalies).
If doing a lot of RV-ing in cold weather and you want to use electric heat, there are several options for installing permanently mounted electric heat. I installed 2 KW of permanent electric heat in our TT which is 30 amps but I also installed a custom demand controller. If you are coming across CGs with low voltage, you can always use an autoformer to boost the voltage.
