269 has used 4130 Chromoly Steel now for the past 4 years and hasn't looked back.
It has three times the strength with about the same weight as aluminum.
We have primarily used 1/2" for areas with little side load or where weight is a concern. 3/4" is used on our chassis although I think we've used 1" as well in the past.
http://aircraftspruce.com/catalog/me...4130square.php
We are surprised that we are still the only team, to our knowledge, to be using this stuff.
The only downside to this stuff is it goes through drill bits and drill batteries like crazy. I think we replaced our bansaw blade this year 1 or 2 times this year as well. We just bought a corded dewault so drilling should be much easier. We always use .035" thickness. We have never had a break.
If you buy this stuff, they give you welding rod as well. Although I don't know if we've ever used it.