You are correct, I was wrong.
After looking at the box diagram from the manufacturer I realized that there are 2 buss bars. One connects at the top and one in the middle.
I only saw the middle buss connector when I first looked but it does have 2.
My concern is if I can split the 240v 50amp dual pole breaker into two 120v 50amp circuits?
All you need to do is run 1 leg off the 50amp breaker to each terminal lug on green house box. ( one wire from each screw on 50 amp breaker to green house main lug connection) No need to chance it to 2 single 50's. Double breakers will both trip even if only 1 side is overloaded. You must run wire rated for 50 amps between boxes. The 50amp breaker is to protect the feed circuit. I bet that's at least a 60 amp rated box on green house. As it's wired you need 40amp per leg. The 20 amp breakers protect the load.
And be careful the service coming out the bottom isn't really fused. The 200 amp main is it's only protection and that looks like 2agw which is only good for 100 amps. Needs reattached and a bushing installed too.
