I have never had a SHB crisis so I don't know if 20 is too many, but it does sound ominous to me. Move your hive into full sun all day and use some kind of trapping method. Lborou uses some cloth traps sold by Bweaver.com with success. Florida is a haven, maybe Heaven, for insects. In my hot, low humidity environment in West Texas, I don't ever see a beetle. That's fine with me.
lazy
I would advise taking some sort of remediation with 20 visible beetles.