I use an ammo can, with the lid removed on teh stove. They are large enough to hold most canopies. Use the powdered RIT dye. Black seems to work best. Tried green on a TigerII and the canopy came out looking like wax paper. Heat it to 135 or so - use the wife's candy thermometer, which she always appreciates. Like has been said, keep it clean, and don't touch. Use tongs, lest your fingers become the color of the dye.
Keep an eye on things, and check often. Once the dye starts to 'take', things go quickly.

I used this dye process on my TF Contender last summer. Still stick the canopy on with dood old slo-cure epoxy. Rust-oleum (brush-on) on the outside for the edging. Works like a charm.