If the brackets were held only to the sheet metal, the screws were likely sheet metal or self-piercing metal screws. If the holes are enlarged, it may be possible to simply replace with a larger diameter screw. If the screws came out due to vibration, replace the screws with the same size to get a good grip on the sheet metal. Since you have some space above the sheet metal before hitting the plywood, you might be able to use a short moly bolt or similar spreading insert which would expand behind the sheet metal and give a better grip, spreading the load of the weight of the motor. A drop of blue thread lock would keep the resulting bolt from loosening in the future. Please report back with questions or a final result.
Ken, Judy, and the Angels--2005 Fleetwood Southwind--2008 Cargo Trailer--2003 EZGO Golf Cart