I don't know how many hours of the day you need the electric heater to be on plus at the same time have the humidity reduced ... but once we needed to dehumidify our RV and didn't have a dehumidifier.
We just ran an electric heater in the RV and the RV's air conditioner at the same time. We found a balance point for a heater's temperature setting and the A/C's thermostat setting such that the inside of the RV was held at about 72 degrees with greatly reduced humidity. This worked like a champ in our 30 amp RV.