If it's under the table it's almost never a good idea because he won't be covered by Workman's Compensation if he gets hurt. Also, you should find out what is being hauled and to how far away, he might fall under the Department of Transportation regulations for hours of service. If he gets...
When I had my central a/c installed in the house I built the contractor told me to never close any vents because it creates back pressure in the ductwork and puts an additional load on the blower motor. The blower is made to move a specific amount of air, if you restrict the outlet for that air...