This looks similar to some we built to use at our conference several years
ago. I have only used one once. It is very heavy (if you are talking 'Portable')
and when I exerted some pressure, it seemed to try to collapse-no way to stand
on it to help stabalize it. My opinion is to use solid(something like angle iron)
pieces that would have a bolt or pin in a bracket that would give it some rigidity
instead of the chain..or holes to drive something like tent pegs through into the
ground(No good on concrete). Or,,,,, try something similar to what I made at welding
class(see articles(Shaky Ed Welding?. I used a very large wheel rim.Its also heavy
but with the vise detached it will roll easily. Ed Aaron