The minimum tread width as per NHRA is 26". As far as the rust situation chrome moly will rust and rust quickly. Where I live in the Southwest it isn't real bad but I have worked on cars from both Coasts and from area's with high humidity and it does rust and rapidly. We just wipe ours down with WD 40 because I don't like to paint the chassis. The most dangerous thing about Chrome moly is that it can and does rust from the inside out. Moisture from various sources can deteriote the internal integrity of the tubing and thin it to the point of it being dangerous. I used to repair many used funny cars and the customers would bring them and the tubing looked real nice on the outside but as soon as you would start to TIG on the tubes they would show the contamination. If you have any open ended tubes (back of the car), squirt some WD 40 in there. Just my 2 cents.
Rick