I am wondering about drilling/screwing into an exterior metal door. I want to install a dart board & back board onto the back of my exterior door that leads into the garage. My worries are as follows: - Will this damage the integrity of the door (i.e. since this is probably a fire door, will this be a bad idea?) - Will this cause the door to lose insulating value for the basement? - What's inside these doors, will it be able to hold a dartboard mounted on plywood?