From my point of view, you can screw the motor as usual, using an aluminium L shaped support, if the motor is an outrunner one, simply turn the "L" 180 degrees looking at it from the top side, and screw the back side of the motor, the screws to fit to the hull, must be below the motor. Just to cool it, being outrunner the autocooling is more efficient, read the motor's datasheet, to know the working temperature and the max one, supposing you need to cool it down, you can use a fan, you can mount it over the motor but not blowing the motor, just blowing in the opposite direction, you will exhaust hot air, and the cool air will replace it coming from below, and cooling the motor at same time, if i can help you some more, simply let me know it