They've been healthy and growing like crazy in this situation for 6 weeks, and suddenly leaf scorch. I keep reading where people are overwatering F. benjamina, so I've been careful not to do the same thing. But if you are correct, then I probably did let them dry out too much. I have a F. triangularis in the same container, but it has much more water retaining soil. Considering it is unaffected, it is most likely a lack of water issue.
I appreciate all ya'lls advice. Maybe I will cut some holes in the lid to allow some heat out while still keeping the humidity high.
I dunked them in a shallow bucket for a good soaking yesterday and then let them drain. The substrate is crushed brick, so it drains right away. Last week I found roots growing out the bottoms of the pots, so I assumed I was doing everything right. But a rookie who refuses to learn will always be a rookie. I'm looking to grow with my pet trees, so, I humbly thank you for your help.