On the ECS (Environmental Control System) front we made a decision to get a CR-2550 (latest generation smaller unit) because it has backup heat coils and the AUTO mode works better than on the CR-7000.
On the APU (Auxiliary Power Unit) front we ran some tests this weekend using an APC SC 1500 UPS. These were done with and without the APC LE1200. With the compressor running on our 550W air conditioning test unit we had very steady power from the DuroMax XP4400. When the air conditioning compressor shuts off it takes an eternity for the SC 1500 to go back online with the LE1200 connected (very strange).
Ultimately it appears that with a minimum load of 500W aside from the UPS load and NOT using the LE1200 the generator works great.
I ordered an automatic switch from shore power to generator power when generator power is present.