Advice: instead of a transfer switch just buy a breaker interlock: https://www.amazon.com/gp/product/B01MV05P2K/ https://www.amazon.com/gp/product/B01MV05P2K/

Advice: instead of a transfer switch just buy a breaker interlock: https://www.amazon.com/gp/product/B01MV05P2K/ https://www.amazon.com/gp/product/B01MV05P2K/ There may be no need for the complexity and space usage of a transfer switch. I would install a male 50amp receptacle (NEMA SS2-50P ?) next to your main panel and connect it to a breaker next to your main utility breaker. Then you install the little metal interlock between them to make it impossible to use both breakers simultaneously ... ... and then you just buy a big extension cord. The 50amp receptacle is nice because it is code compliant for residential and it allows you to connect other power sources in the future.