I have a similar project:
My plan is to:
- Strip out the insulation on the roof, and other affected parts.
- Jack up the roof with four pole jacks, and a 1/4" sheet of plywood, cut to fit the trolly roof, and something to keep it from sticking, (poly?). I plan to jack it an inch or two higher then orignal to account for some sag after I remove the jacks.
- Grind the cracks till they are paper thin at the join, and tapered about 3" on either side of the crack.
- Use polyester resin and glass mat to fill the 6" wide seam.
- Grind smooth, more or less.
- Take down the jacks, maybe one at a time.
- Grind from the inside.
- Lay more glass on the inside.
- Grind smooth from the inside, more or less
- Sand the outside in preparation for paint
Glass mat, which I will cut in 6" wide and smaller strips.
All available at Princess Auto.