The way I read this is that you have a device that will operate from 18 to 32 volts, pulls 180 to 750 mA, and you want to operate it from a 24 volt vehicle system. Is this correct?
If so, then a voltage regulator (designed for vehicular systems as itsmoked suggested) and/or MOV (rated for 24 volt vehicular system) on the input may be all you need.
However, from experience I know that in some heavy industrial vehicular environments - particular near mines that vehicles can be jump-started from arc-welders or 80 volt DC mining carts (fork lifts, etc). Equipment handlers will resort to many 'unusual procedures' to keep schedule when batteries are dead and it's cold enough to gel diesel. Such situations are outside of normal "load-dump" considerations. If this is a possibility, then you need a transistor/zener circuit that opens when a certain voltage is exceeded, or a protection module. By protection module, I mean that someone, somewhere, probably had a module designed to protect devices used on an industrial vehicle - try a google search or talk to the equipment supplier for suggestions.