I made my "portable" vise stand with a round foundation, such that it could be tipped and rolled around the shop...or further. But that it's probably not nearly as portable as your setup, nor as stable.
The foundation is a brake drum from a big truck, then a 1/4 flat plate to which is welded a 6-inch galvanized well-casing (about 3/16 thick for those who never saw one) topped by another steel plate and a vintage 4" machinist vice. Stability is limited, I brace my leg into it to counter-act aggressive filing when necessary. Something makes me think it's ~200#.