I am an HVAC guy so I will recomend this. Since most of these coatings put out fumes caused by the cemohal recation you do not want your air handler running at the time of aplication and during curing. Here is why. If you a ruinig a heat pump sytem or gas fired this is what can happen and quickly I may add. The fumes are cuastic to the evaporator coil since it is alluminum and copper. Second if you are using a gas fired unit and the heat exchanger is not high quality satinless (any Janitrol unit) this will cause rust leading to cabon monoxide poisoning later. Allso if it is a gas fired unit and the unit is sucking combustion from the controlled area and not from the outside as it should be. You and your building may find out what it feels like to be a space shuttle heat shield and quickly .
Now to the sytem set up. Since you mostlikly want to wark on you vehicles in winter I recomend that you have your Hvac tech put in a a duct from the out side so as to bring in fresh air this will be run to the return air so that it mixes fresh air in constantly. Thus diluting any fume that may build up. You could spend the extra money to ge a mixing box wich takes some of the preassure side air runs it through a heat exchanger while it is drawing fresh air this also dehumidfies the in coming air. All ways run more make up air than exhuast so your building stay pressurized. really helps with drafts.
what you may want to do is heat the building with the unit prior to the aplication the use cheap box hear and fan to keep the air flowwing stay until is cures.
I hope this helps.