@S&k we use a Seitz bunk net for our little fellow. If you google it you will find it. Works great, always with the van, just tucks under the bunk during the day. They are more expensive than the portable rails though.
we just used to put a pillow or 2 on the floor until our little one grew up enough to stop falling out of bed. Usually fell out, then got back in and never even realized it.