That's a potentially dangerous mix if you get it fairly strong, so "stand back" is good advice. That foaming action is a strong chemical reaction. I'm not saying "don't ever do it", but mixing an acid (the vinegar) and a base (peroxide) should always be approached very cautiously.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC