Everyone I know who has tried it says the Yankee tank is a disaster. Don't do it.

The HP Combi-Plan tank has its admirers, and Jobo is another option in current production. I use an older Nikor stainless steel tank, which is no longer made. Each one of these options seems to work for some people and not for others and has some inherent advantages and disadvantages. Any of them can be loaded in a changing bag or tent of sufficient size.