I am thinking about mounting an April board with an Env Tail in an aluminum box that has magnets glued to it so it can be attached to metal without screws.
Will the magnets cause any problems with the board or the sensors?
No, but the metal box might affect the WiFi.
It should pass through, but perhaps the distance is impaired?
I was thinking that as well. We will be using a MiFi device that will be very close by, so I hope we will be ok.
Thanks.
A very strong magnet very close (<10mm, probably?) to the inductor on the april board could saturate that and cause power issues… but that’s pretty tricky to arrange in real life 
The box is likely to affect the antenna, though. A plastic box would be better if you have that option.