>Any Ideas as to the cost/ feasability of an onboard suppression system?

Not a bad idea, cheaper than a 'new' bus.  Maybe... firmly clamped dry chem
extinguisher clamped into the engine area with a thin steel cable led to
rear seat for a pull handle?  Rig cable so first 2" of pull gets out the
pin, rest squeezes the clamp.  Could activate it standing outside by sliding
door.  Should be cheap as it gets.  Halon systems are available, try
Automotion (Porsche) catalog, figure on $400 range I think.  Cleaner than
dry chem.

bye, Tim