I've worked with fiberglass in the past. It's some nasty stuff, the resin stinks, and the particles from cutting fiberglass isn't something you want to breath in. Make sure you wear proper protection, and work in an area with great ventilation.
I think I understand what your looking to make. Is it something along the lines of the hatch cover in this video? Only larger? probably the easiest way to build this would be to make a plywood version of the cover and glass over it top and bottom (encasing the plywood). Round over all the edges so the glass can wrap the corners. as far as materials, you'll want roughly a gallon of laminating polyester resin, 4oz of Mek-p (hardener for the resin), 2 different types of glass (1.5 oz csm aka chopped strand matting, and 1708 biaxial). You can buy these rolls in different widths, so you'll need to figure out how much you'll need. Figure on laying 3 layers of csm and 1 layer of 1708. The order should go like this: csm, 1708, csm, csm. youll want to use this same laminating schedule on both the top and bottom of the plywood hatch. Use a solvent resistant roller and chip brushes for wetting out the glass, and don't worry about any excess glass strands hanging over the edges. That can all get trimmed off after everything is cured. because this is a laminating resin, after the glass has set up you'll need to apply a light coat of pva (poly vinyl alcohol). Think of this as a liquid plastic. Poly resin will not fully cure unless the surface is sealed from the air, the pva will do this. Pva is water soluable, so the following day wipe it down with warm water and a scotch right pad to remove this film. Sand the glass smooth and topcoat with either paint or gelcoat. when sourcing the materials, do not get the resin or glass from a big box or automotive store. It's poor quality. Here are some sites I'd recommend us-composites.com expresscomposites.com fibreglast.com the poly resin needs to be catalyzed around 1%. Figure roughly 10 drops of mek-p per ounce of resin. Depending on the temps, you'll have roughly 10 minutes of working time per batch. This is at 70f. The resin needs to maintain a minimum of 65f during the cure cycle which can take up to 24 hours to completely do its thing. If you have any questions just let me know :-) I didn't think that this info would be something that others would find interesting which is why I suggested sending me a pm ;-)
I can only tell you what I have been charged for a similar job. I had some interior 6 panel doors stripped and refinished. Bids varied from $200 to $500 per door, so a pretty wide range. The doors were stripped and finished with opaque tinted nitro lacquer.
I'm also wondering about the balancing. If they are clean and ding free, the balance should not have shifted. That is something I would run first then look into balancing if it needs it. With the bearing on the rod. Spin it and mark with a crayon where it stops at the bottom. Do this a dozen times. If it keeps stopping with the same area down, you may need it checked out. As far as rubber vs urathane.. it's a crap shoot. Some say they are superior, some say not a penny the better. I have only used rubber in the past.
I can't figure out why they would need rebalancing. Are the tires flat like Euro saws, or crowned. If flat, you probably need to get them from Northfield. Are they glued on, or have a tongue to fit in a groove like a Centauro/MiniMax?