depends upon whether you are doing one, or more. also their sizes make
a difference.
i have the threaded rods system and it works well, depends upon what you budget is.
another thing to do is to make your own jig. four bits of straight lengths
which have holes drilled in them for movement, then corner blocks which could be wedged for final adjustment.
otherwise spend the budget and get the bessey corner clamps
VERY NICE :tool:
the real thing is how many you are going to make, otherwise, you could just use normal longish clamps and corner blocks which could be two separate bits of wood which actually fit at the corner.
all the best
paul :wink: