Very important is to raise it up off the floor--whatever kind of heater you use, be sure any "source of ignition" be it flame or spark (ie, pilot lights, ignitors, motor brushes, contactors, plugs, etc) is at least 18" above the floor. That is the typical building code requirement, but a bit higher won't hurt any. The idea being that flammable vapors (gas fumes, etc.) are heavier than air and collect on the floor where they can ignite. I set my wood stove on top of cinder blocks turned on end.
Be aware of side clearances also--typically there is a 5' clearance to combustible sidewalls, but also typically that can be reduced to 16" or so if you mount 3/8" concrete board on 1" hat channel on the walls. Talk to a wood stove shop if you are not sure, but be aware that all bets & specs are off when using 'used' units. Also be aware that the latest NFPA [fire dept] codes prohibit 'solid fuel appliances' in garages altogether....which may affect your house insurance liability, should you have to make a claim someday.
You will probably also need to pipe in combustion air from the outside--wood stoves draw a lot of air to burn, and if you rely on getting it from inside the garage, not only will your stove not burn well, but it will be sucking cold air in from outside to burn. As well as potentially flammable vapors....
Your engine needs air to breathe, right? So does your stove.
All that said, in my 800 sq. ft. detached garage with mostly insulated walls & ceiling, on a typical (let's say 20*) Colorado winter morning, after a week of no heat, I will go out first thing and fire up my small sized (approx. 14"w X 16"h X 24"d) residential free standing Vermont Castings wood stove, then go back in the house and have breakfast... In less than an hour when I come back out, it will have "broken the chill" and the fluorescent lights all come on. Within another hour I can work comfortably with longjohns & flannel shirt. By 5 or 6 hours later, I'm down to a t-shirt and bandana to keep the sweat out of my eyes......
I have bolted an old reciprocating fan (like the ones in old movie detective offices) upside down on the ceiling above the wood stove to circulate the air. Works great. Nice in the summer too.
John