ramses said:
What all else is there besides the fenders that ill need? What size tires are on the red one and the white one? What will happen if the wheels arent spaced away from eachother far enough?
I couldn't even tell you the names of the parts you'll need. You should be able to get an exploded view of the fender detail from the parts counter of a GM dealer. There are braces, covers and fillers. The bed is double wall construction. Along with finishing off the installation, these parts hold the inner and outter walls of the bed together after the walls are cut. I think you'd run into some problems at highway speed if you were missing some of these parts. You can see some pics. of what that cut should look like.
http://blog.mannon.com/archives/000019.html
Unlimited Fiberglass makes an aftermarket dually fender:
http://www.up22.com/chevytruck.htm#GM-201R/L
I have a pair sitting in my garage. They attach in a different manner than factory fenders and don't seem to require the same parts as the factory fenders. I never used them, so I can't say if they work or fit well, but that is another option.
As for the tires on my trucks. The brown (or red as you called it) truck has 15 x 36 tires. The springs were moved into the frame rails, the bed was tubbed, the E-brake cables reworked, the drums turned down and custom wheels built.
The black truck is running 33 x 12.50 tires. It has turned down drums (not as much) 4 bolts at the inner fenders were trimmed to clear the tires and custom wheels built.
The white crew cab was purchased as you see it. Those are 12 x 36 tires on stock rims at the back with a spacer. It's a tight squeeze over those rims and the tires hang past the fenders a lot. I think it might be over the legal width. I'm going to be changing that one to custom wheels as well.
Dremu's got it on the spacing of the rears. Rubbing rears is a no no.
Good Luck,
Eric M.