I installed a firewall mounted booster/master cylinder so I welded in patches for the old master cylinder hole. Did the same for the trans access panel, gas tank holes, clutch/brake pedal holes, etc. Plenty of room underneath to access the automatic trans oil cooler lines. The underside of my cab was plastered with some kind of nasty undercoating which did a good job protecting the metal where it stuck. I removed all the old undercoating, then brushed Rustoleum primer and topcoat. Looks good and should protect for a long time.
