I like the floating island idea and I hear it's a great setup for Seminatrix, Regina (alleni and regida, especially), and Farancia. I'm sure the more aquatic Nerodia (floridana, cyclopion, taxispilota, rhombifer) would do fine in them also. I'd have to see your plastic "bridge" setup to fully visualize what you're talking about. Sounds like a neat idea, though. My clarkii of both ssp. are doing great in pretty typical terrestrial setups.
This is my clarkii clarkii tank.
Here's the Mangroves humble abode. I use sphagnum and cypress mulch in their tank to increase the ambient humidity which I don't feel the Gulfs need as much.