Depending on the model you select, the can be either mounted inside the vehicle with the sub floor built over them or they can be mounted underneath the vehicle. It is a good idea to think about what you will use before you design the interior of the vehicle in case you need to make room for it.
You won’t be able to just reach into your pocket and dial the locksmith if you are living in a vehicle down by the river. Even if you are always cautious about picking up the keys when you go out, you need to make sure you have extras in place. If you never need them fine, but if you ever do you will be very grateful you took this advice.