Yeah, I'm not sure this is a very good idea. I may have no experience with this (unless being in a car with somebody who had an open cup of coffee counts lol
), but based off the episode of "Tanked" that was previously mentioned and some basic physics, I can tell you this is probably not a good idea. Try driving a car with a tank full of water, the water will slosh everywhere and stress the fish out, it might break the tank, the RV may not even be able to hold that much weight, the tank with water will be 800+ pounds in such a small space. If I were you I'd have a friend or family member take care of the lungfish, you will not be able to provide it with a large enough tank in your situation and the fish will get very stressed out.