Rocket mass heaters, by their nature are HEAVY. Can the floor of your bus stand the weight?
The link you referred to has one monumental horror, the flue pipe. All those kinks are a disaster, with no access for cleaning. It might be better to have a heat exchanger chamber, but it needs access to all the flue sections.
The blog shows just a steel box stove, but I would only have one if it had a glass door, so you can see what's going on.
If you have no experience, IMO you need to get someone who has. It's not the sort of thing to learn from a forum in less than a week.
