I have purchased a used rv and have two ac units which are duo therm. I would like to know if I can replace the thermostats with another brand?

Most duo therm units used a Robertshaw stat ( a little square one ) If you remove the cover from the thermostat you will see some small screws that hold the stat to the subbase, by removing these screws the stat will separate from the subbase, now you will see the wires, attach these wires to new stat on same terminels as old. You can replace this type stat with most stats that are mechanical or battery operated thermostats. There are RV's that do use a line voltage stat, by removing the front cover it will usually indicate the voltage, always turn off the power first.