No bed

If you really like camping and/or minimalism, it's possible that no bed is the right bed for you. Starting from the idea of your vehicle as a metal tent, you may be able to sleep without a bed, either directly on the floor or with a simple pad as if you were camping in a tent. Most people will prefer something more than this, and it will be required in cold weather if your vehicle floor is not insulated adequately. If you think floor sleeping is a possibility for you, be sure to test it thoroughly before committing to it when planning your build.