Best bet for an IB is to use the basement (
Bassment?

) or attic if you can. One method is to cut a hole in the floor or ceiling, create a 5-sided box & mount it in the hole, with the opening into the room but the rest sticking into the other space. The box should have holes cut for the woofers, and they mount to the box, radiating into the box and out to the room. The IB concept utilizes this huge amount of space as effectively an infinitely large enclosure. Note that the space you choose won't be of much use for anything else (don't plan on siting your den in the attic that soaks up the backwave of all those woofers!

).
Mounting a standard sub in a wall is generally a Very Bad Idea. Unless the model you choose is designed to be used that way, you'll have a mess. At the very least you'll get a lot of vibration & noise, and walls aren't the optimum type of space for speaker drivers.