sorry man but cutting a couple of wholes isnt going to cut it. your temps with a 400 are easily going to hit 98 +deg in 15 minutes.you must,must, have some sort of an exhaust.if your space is small,instead of buying an intake fan and exhaust fan you can buy a larger exhaust fan and have the holes you mentioned at the rooms ground level and it will "if your rooms is well sealed" pull in fresh air at the same time as it exhausts the old air from your room.not to be a party pooper but you mentioned that this is in a laundry room? humidity from a washer and dryer is with out a dount going to own you.well absolute best of luck to you.