I use the F-10. And notice a slight smell to it. but certainly not what you described, unless he sprayed
it all over his house- gallons of it, right before you arrived.
Once it dries, I can't smell it anymore.
I don't have enough experience with snakes to offer you any other tips or info.
but just want to say "kudos" to you, for taking on such a big task. I sure hope you can breed
them in the future and make some money- you certainly deserve it, after taking on this big of a rescue.
Good luck- hope they are all healthy and in new rack/ homes soon!