Although transfer switches are designed to transfer under load, arcing does occur under all loads and the arcing is heavier and more severe as the load increases. Arcing causes corrosion of the electrical contactors within the transfer switch which results in eventual transfer switch failure.
So, should you use your transfer switch under load? The answer is that is exactly what it is designed for. But, since most all transfer switches are inherently slow in their load transfer (defined as the momentary absence of power during the transfer from shore to generator or generator to shore), your air conditioners, microwaves, and clothes washers will cycle off during the transfer which is not helpful. Thus, its better to power off the heavy loads before the transfer as they will just cause more arcing with no other benefit which reduces the service life of your transfer switch.
Also, keep in mind that all RV transfer switches are set from the factory as being generator preferred. What this means is that the transfer switch will activate within a preset time (30 seconds to 2 minutes depending on your transfer switch) switching the load from shore to generator even if your RV is attached to shore power.
Your results may vary as some transfer switches have DIP switches to adjust the generator preference to shore power preference.
Jim,
Then you best option, provided that you have a Refrigerator opening of sufficient size, is option 2b. This option is vastly less expensive than a new Norcold refrigerator, is not a fire hazard, and is very efficient with a massive interior space uplift versus the Norcold:
Another equivalent choice of a 12V compressor RV style refrigerator that has the interior storage and features of a residential refrigerator are the RecPro RV 12V refrigerators. These refrigerators have doors that will not open when you are on bumpy roads just like your existing Norcold and they include standard mounting hardware so that you don't need to do a custom installation. The only catch is that they may or may not fit your existing opening, so measure carefully:
https://www.recpro.com/rv-12v-refrigerator/
This option will cost ~$5-$10 per month for electricity if running full time
