What's the best way to handle the rust in the trunk hatch area by the glass? Do I grind the metal til the rust is gone and end up with a whole? Or is there a spray that prevent's rust. It's not that bad but i want to take care of it before it spreads.
Where, exactly, is the rust? Is it along the edge of the glass/rubber gasket? If it appears to be originating from under the rubber you will have to remove the glass in order to stop the rust completely in it's tracks. Removing the glass isn't too bad, it's getting it back in and seated properly which can be a little tricky. Mostly just a time consuming type of tricky but can be done with standard tools; flat head screwdrivers, putty knife, wire, some creative swearing and a few objects handy to hurl against a wall.
Depending on the location of the rust, it may actually be a little more severe than you're thinking. IF it is under the rubber surround (along the bottom edge of the glass?) it's most likely originating at the seam of the outer and inner metal skins. In this case do some investigation of the inside also. If there's rust on the inside at the same location it will be a little more work to repair.
If the rust is only surface or only on the outer skin you can grind it down with a wire wheel. Just be sure to remove EVERY single bit of the rust. After grinding use some POR 15. After using this stuff just once I'll swear by it. (www.por15.com) Depending on the severity of the grinding will determine if you'll need to use any filler to level the surface before painting.
If the rust is in deed more than just on the surface or you find something on the inside, your only hope of stopping it is to cut out the infected area completely. A few years ago I found a decent hatch in a yard with some minor rust right in the area I've been describing (under the glass rubber along the lower edge of the glass and along the seam of the inner and outer skins). I cut out the infected metal, about 4"x4", on the outer skin. After cutting it appeared that the inner metal at the same spot was salvagable with some grinding. I welded in a new piece of metal and feather filled to match the contour. Painted, buffed, installed glass, swore and everything looked great. Unfortunately the rust came back a few years down the road because I didn't use enough precautionary measures.
Use these rust prevention methods if you do need to cut and weld.
1. Remove ALLLLL the rust!
2. Use the POR 15 metal treatment before painting. This will essentially seal the metal from any contaminants.
3. Be careful not to scratch or chip the paint when reinstalling the glass.
4. 3M makes an internal body panel rust preventor. For the life of me I can't think of the actual name right now. It comes in a large spray can and can be bought at any automotive paint supplier. The rust prevention material is amber in color when sprayed. It's not the black, rubberized under body coating. This stuff sprays on in a heavy liquid form and sets up and retains and sticky, waxy feel. It's ideal to spray this stuff along all sheet metal seams especially in the hatch. Spray along the seam of the inner and outer skins along the bottom edge of the glass, along the bottom edge of the hatch, around the lock tumbler when it's installed and anywhere else you can fit the extension tube. Use only AFTER painting.
Most of the rust in MKII and Celica hatches is caused from the inside out. This is due to water finding a way to enter the hatch either around the lock cylinder, spoiler mounting holes or getting around one of the rubber grommets which wires pass thru. The water sits along the bottom seam and slowly over time penetrates the metal. Using the 3M spray will seal these seams and not allow water to infiltrate the metal.
Either way will take time but a little time spent now is better than time later spent weeping when the rust has caused the car to look like a leper.