Roll Hoop Back stays and cross brace.

[brainbug007]

Personally I used CDS as I found it easier to source off ebay than ERW that had thick enough walls (3mm+). I got 2.8m for about 30 quid including delivery which didn't seem that bad and would cover the braces and cross section. I would think making it out of 50x50 would be a bad idea as surely the welds wont be strong enough to hold in the event or a roll?