The only way i have ever heard of quarters wanting to wrinkle is on acid dipped bodies on factory prepped high powered drag cars. I believe the sox and martin Hemi duster was so thin, they glued styrofoam to the insides of the quarter skins to prevent this. Unibody construction is pretty strong, however when adding a high powered small or big block you need to stiffen it up in key locations. Multiple ways to do subframe connectors, torque boxes, lower rad supports etc. If interested in how i did mine, and how to set up the body shell to keep it square during this process , let me know. Glad to help
