Hi,
I was parked about 300' from the power meter on a Ranch, and the well was wired with $8 wire to a 30 amp circuit breaker. I would have 120 volts with nothing running, and the drop would be about 15 volts when I turn on my A/C. This was solved by using a 12 volt booster transformer. I think you will need the same thing.
So #8 or #6 wire from the house to the RV location, and then you will have #10 wire to the RV itself for about 25'. My guess is that you will have about 12 volts drop across this long wire.
If you where to use #12 wire suggested above, you would see a voltage drop of over 24 volts.
Anything below 100 volts, and the compressor will be drawing so many amps, it will not work above about 80F and will trip on it's high amperage overload until it finally dies.
I have run my A/C at 105 volts input, but not for long. I will soon get out my voltage booster.
When I was living on the ranch, I would plug in the RV to the RV receptacle, and the voltage booster into that. The refrigerator was plugged directly into the shore power 20 amp receptacle, so it would NOT be boosted. When I was running nothing in the RV, the voltage would rise to 132 volts, an un-acceptable high voltage to run the refrigerator electric element. But the input voltage of 120 was fine when not running the A/C and the water pump was off. If the pump cycled on while I was running the A/C in my RV, then the inside voltage would drop to about 118 or 116 volts (remember boosted by 12 volts) and the refrigerator still ran fine on the 100 or more volts that it gets. Problem happens when 130 volts is applied, the amperage goes up and wattage goes WAY up, causing the tubing to crack, and ammonia to leak.
So it is better to run the refrigerator on gas only anyway. The 3 amp electric draw will also drop your voltage to the RV by about 2-3 volts!
You might want to buy a 'kill-a-watt' meter. It will be able to stay plugged in all the time in the RV, and if voltage goes to low, you can shut off the A/C and protect it from damage!
http://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU/ref=sr_1_1?ie=UTF8&qid=1442115727&sr=8-1&keywords=kill+a+wattBest $18 you can spend on the RV! Plug it into a receptacle near the dining table, or in the living room where it is visible, so that your guests can monitor the voltage under load while running the A/C unit.
You might also want to buy a 'autoformer' Hughes autoformer will take the incoming voltage and boost it by 3% and measure the incoming voltage. If it drops to say 110 volts, it will automatically boost the voltage by 12%. A 30 amp version is about $350 - $400.
I built my transformer with a 500 watt 12 volt isolated circuit transformer, much less expensive, but not automatic change from low to high voltage output like the Hughes unit. This is a transformer rated at 40 amps at 12 volt output. The output of the transformer is added to the input voltage, so I get 120 in and 132 out! When the A/C was on, I would get 108 in and about 118 out.
Good luck,
Fred.
