Marlopolo, as a structural engineer, I must say you did some ingenious work in delivering the load to the strong floor foundation through column action (table legs) rather than delivering it to the very thin walls via shelf supports -kudos. Why only three legs? Is it because a 1x4 would block the door opening on the right? Could you get a shot of the support detail, cause you have me interested in this mod!
About a swivel front seat, I have seen the topic come up on other threads, so maybe a search in the Class C Forum as well as the Camper Van forum (where people may have customized a rig to be an RV).