I'm not that concerned about it to go to those lengths

I thought the silicon bags kind of worked like the moisture traps you can buy for caravans etc which I use in the garage for my motorbike), guess I wasted my time then. Didn't cost a lot though so not wasted much
Which camera is this? My understanding is that you can have AF-ON for BBF, and then you can have AF either on or off for the shutter, but if you have it on the AF mode will be the same for both back button and shutter button?
The whole point of having BBF is so that it acts as both continuous focus and single focus, i.e. you press and hold the back button for continuous focus, or press the back button to focus and then release to recompose, having the shutter button AF disabled then means that you won't then refocus as you release the shutter.
I don't see how you can have the focus mode set to two different things at the same time, what happens if you keep hold of the back button whilst pressing the shutter, the camera won't know what to do?