RE: HELP WITH ST. CROIX/CRESSLINE LONG EZ KIT
Put it in hot water and let it relax back to the proper shape, then lay some light fiberglass on the inside. You can use epoxy to bond it to the inside. Some may say to bond the glass with MEK to the plastic, but if it's as thin as you say I wouldn't try that.
Mylar film is very strong in tension, so I would say Mylar covering would be fine. I made a Zip launch glider that I just butt glued the wings together then used the Mylar overlapped at the poly breaks, it goes from 0 to 80mph in about 10 feet, so it takes a lot of gees.