Gary Lewis asks whether varroa are like ticks in that they can wait
around for long periods of time before needing to get to a host. He
believes in that case the open mesh varroa floor wouldn't  work because
the mites could eventually crawl up again into the hive.  Dave Eyre
suggests that the hive bottom support should be made as a box of treated
2x4s upon which the open mesh bottom board should be placed.
 
I would suspect that mites are not like ticks, in that they need to feed
regularly.  However, they are very mobile, and might well get back into
the hive.  Why not use Dave's bottom board support (which is fully
enclosed, if I understand it right) and coat the inside of it with
vaseline (petroleum jelly) or some other similar product?  The mites
would fall through the mesh below the hive, then be unable to get back
because of the greasy hive support and soon die off.  Ants also would
not be able to get in because of the petroleum jelly.
 
Ted Fischer
Dexter, Michigan USA