Hi Larry,
Welcome to school
The size inverter (rated in watts) is a function of what all you want to power "at the same time". "Most" electrical equipment has a plate or stamp on it (back or bottom) that has the max current draw in "amps".
Ohm's law is used to convert amps to watts. That law is amps x voltage = wattage. My guess is that your compressor is in the trailer in storage so no access to it for reading the plate. But if you know the model number, we can look it up. But let's run through an example of how you would determine what size inverter you'd need for a compressor that had a 10 amp max current draw rating. 10 amps x 110 volts AC = 1110 watts of power needed at max current.
So if you wanted to run only the compressor or anything that draws less than 10 amps or 10 amps in aggregate, you'd want a compressor that is rated for "at least" 1200 watts continuous. The word "continuous is key. Most ratings on the outside of the box of an inverter are the "surge" watts that it can deliver for a short period.
Would you ever need to run your compressor at the same time you are running other items in your RV? My guess is no. And in fact, to keep the battery bank you will need to feed the inverter, I'd suggest you do not use the compressor when you are powering other items. This way, the compressor load does not need to be added to the "other items" load when sizing the right inverter and battery bank.
I have mentioned battery bank a couple of times. Inverters invert DC (direct current) power from batteries to AC (alternating current) for use by AC items (like your compressor, TV, apnea machine etc.). How many batteries you need is a function of how much "run-time" you need for your AC powered items. More time requires more batteries.
Then with batteries, you need to put the power back into them (recharge). Some RV inverters have built-in charge circuits and when plugged back into shore power, can recharge the batteries. Other non-RV inverters like a 1000 watt model I bought cheap at Costco, do not have charge circuits in them. I bought this to use in my truck with the truck running. If I were to use this in the RV and draw power from the existing RV batteries to power the inverter, once connected to shore power, the "converter" in the RV will recharge the RV battery(ies).
Some people who use inverters in their RV, recharge them with solar panels and a charge controller.
So many options, so many things to think about. Have you considered a 3,000 watt generator for the back of the truck? You could get one of those cranes from Harbor Freight like Forest has and use it to load your genny and install/remove your hitch when needed. With a gen of that size, you could power the whole coach and 1 air conditioner. Something to think about.
Jim
