I purchased a Honda EM3500S, 3500 watts surge, 3000 watts continous. We got it primarily to run the air. If you want to run other appliances at the same time of the A/C start up, you'll need to add their loads to the A/C's max load and may need to get a larger unit. This size is okay for our 13. 5K BTU air, lights and water pump for dry camping. As a reference, a 30 AMP circut handles about 3450 VA (current times voltage) continuous. More current means more $, more size and more noise.
I bought a 20' RV power extension cable and cut off the female end with about a 2 foot from the end. Purchased a plug and rubber boot at Home Depot to mate with the generator to make a 2' adapter. I put a receptacle like the one on the generator on the 18' cord. Now I have a 2' adaptor for the main RV cord to connect to the generator and a 20' extension for the main cord when the 2' adapter is installed that allows connection to either a standard 30 amp RV outlet or, when visiting friends, 115 VAC with a standard RV 115 VAC adapter.