"How do you mold the carpet around curves? wheel humps. tranny humps etc?"
Well, you don't.
Much like making a garment, I would imagine, you rely on slits and fitted pieces.
I found it easiest to work with stiff paper as pattern material when I made carpets for my Midget, where I didn't have the old carpet to go by.
Basically, if you can make stiff paper fit correctly, then the underside of the carpet will fit just the same.
Any stitching and edging needed can be done by most upholstery places or carpet stores.
It's good fun to get into and gives you a great sense of accomplishment when you see the results of your labor.
Good luck!