TOBOR V was made from Bosch (30/30)...
The stuff is fun, just like an erector set. It's strong too. If you plan on getting very physical (ramming people), then use the 30/30. If you plan on just stacking boxes and shoving people on the side, 20/20 should be fine, but it may bend a little. We used 30/30 but still bent it (about 1/2" of a bow) when we rammed a goal in a match last year @ ~12fps (we bent that bar with the polycarb bumper on it).
It's better to bolt the stuff directly, like how we did it. Brackets suck. We never broke a bolt.