The chains tend to rub bottom on the HDPE Attex bodies on the right side especially. I saw one of the Gerber's machines with a 1" piece of lumber under the frame on the right side to keep the body from warping up and allowing the chain to rub on that side. The plastic tends to form up to the frame on the right because there's no real support for it- the inside frame member is too far to the right and won't keep the body down. I've used some pieces of oak flooring to do this and it works well- just drill a couple small holes in the round members so you can screw the wood into place.
Good luck!
Stuck in the seventies- not in the swamp.
(6) Attex, a Hustler, a Super Swamp Fox, (2) Tricarts, (3) Tri-sports, a Sno-co trike, 3 Dunecycles, and a Starcraft! ...so far