When mounting casters, I prefer to use ones that don't require a large hole to be drilled. You don't have to dramatically modify your cab and there is no problem with air leakage. Mesa Boogie uses a type that uses a regular castor but it slides onto a mounting plate. This allows you to remove them when you want. They sell them at their site
. A similar product is also available here
. This company offers a large and small caster plate. It's a neat system.
Another option is to buy a dolly or hand cart from a hardware store. This way you don't have to modify your cab.