Mellotronists

Hello - I'm now preparing to install some mounting brackets that I've 
made for the bottom of the spill box on 1407 and it's going to 
necessitate drilling through the bottom of the spillbox to attach the 
brackets.  I'm using some #10 machine screws, and I'm wondering if the 
head of the screw can/will cause any magnetizing problems inside of the 
spill box when tape is running through there.  I've noticed that the 
side mounting bolts were recessed with a forstner bit so they actually 
sit below the surface of the wood.  If the bolt head will cause 
problems, would it be okay to simply line the bottom of the box with 
felt or some other material?  It doesn't look like the bottom of the box 
is all that thick, so I'm a bit hesitant to attempt to make recesses for 
the bolts.

thanks,
john