What you need:

Good latex (I use tap plastics mold builders latex (www.tapplastics.com) its strong and wont discolor like the cheap mask makers latex)
Cheese cloth (home depot, or a roll from mc master carr www.mcmaster.com part # 7340T12 if your doing a lot of corpsing)
Stretchable spider webs (the cheap shitty ones from any Halloween store, but not the glow in the dark type) (not a requirement, but good to try and great for detailed coverage)
2” disposable chip brushes
Scissors
latex gloves

Start off by cutting a bunch of different sized strips of cheese cloth (big and sharp scissors will make your life easy) and lay them in separate piles according to size.

Prepare your skeleton. Pose it in the required position, and add an armature if you need it to sit un assisted. I personally weld the armature to the buckys steel spinal post and or attach it using white 8-10” tie wraps.

Next add the cheesecloth around the structural elements of the skeleton (ie affix fingers, arms, legs etc to the armature or itself) and don’t even think of the detail at this time. You want to focus on strengthening and holding a pose, not the final look.

With the cheesecloth added to all structural parts, start applying latex liberally to saturate the cloth and underlying bone. Cover it completely then allow it to dry overnight (or in colder climates 48-72 hrs). The latex should be a transparent yellowish color and no white areas should be apparent.

Now that its dry, go in for a second application of cheese cloth but this time go for detail. Rip and stretch the cheesecloth to create rotted flesh and if your using spider webs, I suggest dunking small pieces of webs into the latex then stretch them out over the corpse in different lengths to create thick and thin areas. Like putting those webs up, the further you stretch them, the better they’ll look.

Once you have the main detail done, allow the latex to dry for a couple hours, then while drying, apply more latex to areas that look weak or where the cloth has absorbed the latex leaving an exposed cloth (although when painting, exposed cloth can look like decayed clothing, so leaving some bare is advised if your going for that look)

Now that the corpsing is done, allow it to fully dry before painting.

For painting, I suggest either airbrushing, drybrushing, or staining the entire thing (or a combination of all 3).

For airbrushing or drybrushing its pretty self explanatory, just work from light to dark.

For staining (which I prefer) apply stain using a disposable brush, and work quickly wiping off stain to leave a light stain, or leave it thick to create dark spots. I prefer minwax’s “provincial”, “dark walnut”, “walnut” and “ebony” for darker corpses, and light medium brown shades for yellowing/antiquing the bones.

With all things, practice makes perfect, so practice on inconspicuous areas until your comfortable with doing the displayed pieces.