RV Parked at Home Questions
I've used a 50 foot, 15 amp extention cord plugged into a 15 amp socket, then plugged the 15 to 30 amp adapter into the extention cord, then plugged the 30 amp trailer cord into that (I was in the street, and the outlet was in my friends garage. No problem using my air conditioner ONLY (well ok, converter, water pump and refrigerator too). The only time it might be stretching it is the AC startup surge, which is brief and not very often.
I would not leave any cord on the ground more than a few days (not that it is a problem, just that good cords are expensive and being on the ground ages them fast), and unless it is daytime and I'm right there watching it, I wrap all junctions in plastic bags to keep any moisture out of the connections. I would also not leave any junction on the ground where it could flood, since the plastic bag treatment is only water resistant, not proof.
When at home, I plug the trailer into a 15 amp outlet at my house (adapter but no extention cord) and use the AC and microwave, plus converter/refrigerator/etc with no problems so far. Does make me nervous though (if AC tried to start while microwave is going, for example), so I'm putting in an actual RV recepticle.
So, to answer your questions, yes, rain can cause problems with external connections. Check out all the rules for outside outlets in the building codes... You will want to have a watertight cover (open at the bottom is ok) over the outside outlet. And you will want to have any other outside junctions water-proofed (plastic bag and duct tape is the quick and dirty way to do it). Leaving cords lying on the ground is personal choice.
As for the type of socket, a 30 amp RV socket is best, followed by a 20 amp socket, and lastly an absolute minimum of 15 amp. This assumes that each of these sockets are protected by the appropriate breaker. The real key here is that whatever cord you use MUST be rated at least what the rest of the circuit is rated. That way, if you should happen to draw more than you should, the breaker will trip, protecting the wiring and the extention cord.
The best extention cord would be an actual 30 amp rv extention cord, with the adapter to 15 amps, if required, right at the 15 amp socket. However, a lesser cord (20 or even 15 amp) can do the job on a temporary basis, assuming that your A/C does not trip a 15 amp breaker, and nothing else is on the circuit.
If your A/C DOES trip a 15 amp breaker, it is possible that an 'easy start' kit (also known as a 'hard start' kit, oddly enough), may spread out the startup draw enough that you can run off a 15 amp circuit. Your best bet is to have a current meter which tells you how much current you are actually drawing with the A/C. If startup is brief and under 20 amps, and running current is 10 amps or less, you should have no problems using a 15 amp circuit to run the A/C.
