A typical spacer heater may have two settings (switches), esp. the oil filled type. The low setting is usually 600 watts and the second one is usually 900 watts with both toggled on being 1500 watts.
A typical 15 amp circuit will allow about 1750 watts if I remember correctly before tripping the breaker. 15 amps x 110 volts equals 1650 watts and 15 amps x 120 volts equals 1800 watts.
The heater is 1500 watts max, thus leaving a little for the lights.
The trick is to use the heaviest gauge extension and as short as possible as there is resistance from the cord. Thus a 12 gauge 25' for example would be very nice although you could go longer with that gauge. If you have say a 14 gauge 50' cord you may only want to use 900 watt max. on the heater.
Needless to say these cords will fit only a 15 to 20 amp. outlet.....which should be normal household receptacles.
You should be able to do it. You may find that 2 heaters spaced out in that size trailer set at about 600 watts (2 x 600 watts = 1200 watts total for heat) would be more comfortable.
For heat, you could fire up the propane heater for a night and use the electrical for lighting, although with what I mentioned it should work ok with the electrical unless the temps drop real low......like about 0*F or so.
I have a electrical heater going this morning in my 1996 T-2053 and it was about 32*F with 4*F outside. It was set at about 50*F, but I'm sure that little heater was working all night (which was below zero) to keep the temp at about 32*F.
Good luck an do enjoy. I say go for it.
P.S. electric blankets work wonders also!