If you buy from a big box or Amazon you will not get real support from someone that knows RVs. I strongly recommend TechnoRV for Sales and Support
https://www.technorv.com/brands/Surge-Guard.html
They have 30A on sale for $209 and 50 A on sale for $299.
These units will shut off the connection or never turn on the connection if there are problems from the power source.