Read and follow the good advice on the Polyphaser Tech.
notes website regarding lightning protection:http://www.polyphaser.com/ppc_pen_home.asp
I take DIRECT lighting hits most every big lightning
storm. With no damage. So do most all commercial
radio stations, Police, Fire, Ambulance, etc. towers.
NONE of these stations "disconnects" coax when a storm
approaches. And all of them that are properly grounded
do not suffer damage from direct hits.
A homemade bulkhead could be made up using copper or
aluminum, But as long as you follow the single point
ground theory you should be OK. (Just attach all
coax switches, Lightning arrestors, etc. to a large
copper or aluminum sheet near where your coax enters
the shack. (A four inch clothes dryer vent makes a
great entry port)
The only problem using aluminum instead of copper is
when you get outdoors. Copper is the only product to
use where it comes in contact with the soil. Most all
soils will "eat" aluminum. You can sometimes get copper sheet from upscale roofing companies.
Use "hard" silver solder to bond together.