Get a few of those big ass oil drums.
Cut the body up into chunks - alternator size is a bit small, battery size is about right.
Fill the drums about 3/4 full with fine industrial sawdust from your local furniture factory. Add diesel oil until you have a soft dough.
Place a few chunks towards the top of each drum, then pack with more sawdust diesel mix until the drums are full.
Top off with a little gasoline.
Light.
The sawdust/diesel mix is very thick, so that the body chunks don't sink, and stay suspended in the hottest part of the fire. It also burns reasonably slowly but at a good high temperature.
A 42 gallon drum burns for about 1 week - less if you perforate the sides of the drums. Easily performed with a suitable rifle.
After a week at the very high temperatures of burning diesel, there will be nothing recognisable left - even the bones will be reduced to ash.