Thanks Peter, good to know someone has used the DIY carpet in the past with decent results, and Yes, cheap as chips

I've been going over the HOW TO in my head the last 2 days on the best way to lay the carpet so it sits nice, flush and pretty over the tunnel down the sides, across the floor and down into the 5" drops. As of now, this is the plan...
Find dead center of the carpet and match it to dead center of the tunnel. Put a few short & small screws through the carpet into the tunnel to hold it in place so I can tug and manipulate where needed.
Please excuse the crudeness of my art... I didnt have time to draw it to scale
Form the carpet over the tunnel and down the sides. At this point I'll probably need a long sturdy straight edge (2x4 or 4ft level) and form the 90° as it meets the floor pan. I haven't tried heating the carpet from the finished side so I might have to lift, heat, form, cool, repeat all the way down the tunnel. Just going to have to see how that goes. Because of the way the tunnel flares out at the back, I'll have to heat the carpet and do some of that tugging and manipulating I mentioned. I think this is going to be the hardest part, but we'll see.
I think just trimming along the outer edge of the pan will do fine, but I'll think about the stuff that Rick posted the link to.
Cutting in for the floor drops could be tricky, I think I'll go this route, so there aren't any easily visible cuts or seams in the carpet. I'll cut the carpet at point A along the side of the tunnel back to line D. I'll cut along the outer rail following that line back to the line D cut. I'll cut some where in the middle of the A/D cut to the outer rail cut and fold those down into the pan, heat along line B and C. Then make up the difference in between with a small piece, maybe duct taped on the back side.
I'll cut a piece to run down the inside and outside of the seat pan drop (blue section). Again, the back of the pan, behind the seats could be tricky (purplish area), but I'll figure it out, eventually. Pictures eventually.