RE: Holes through the chassis
Seconding the comments on the dangers with large hole saws on metal, use
great caution.
A better approach, if you can get a hold of one, is a conduit punch,
sometimes called a chassis punch.  They can usually be rented from a
local tool rental house. Very expensive to buy.  Slower but much safer
to use, especially in confined areas or going through an irregular surface.
While on this subject, a trick I picked up recently.  Problem:  You have
, lets say, a 2" hole that needs to be a 3" hole.  Standard hole saw is
no good, nothing for the pilot drill to go into.  Solution:  Assuming
that the mandrel on the hole saw is removable, mount BOTH a 2" AND the
3" hole saw on the mandrel.  Now the 2" saw acts as the guide and the 3"
cuts out the new hole. BTW, this does not work well if the step up is
very small, like only an 1/8" or so.