Mike;
Rex is right, long skinny bars tend to bow out sideways when placed in compression but you could increase the diameter of the bars to reduce that. Large diameter light gauge tubing is better than small heavy- wall tubing.
Where possible it would help chassis stiffness to weld on thin sheet steel stressed panels. They do interfere with access but you can cut out holes for access and if you use a doubler ring and tight-fitting bolts it will act like a one- piece panel. Don't forget that torsional stiffness is important, too.
Your project is looking great!
Regards, Neil Tucson, AZ