I have concrete all around the area making it very hard to mount it to the house So I thought I could sink a post about 5ft away from the spa and mount my 50 amp gfci

A post should be fine but we should know where you live so as to check codes

Marysville ca

CA has way too many unique codes for me to keep up. Call your local building dept to see if they allow it. Its fine for Illinois, but we shake less.

Thank you for your efforts I will call the building dept