This is gonna sound crazy....
I have cooked a couple dozen whole hogs and even a handful of cows using only hot rocks and banana leaves. Start a couple of Bon fires. When they get going pretty good pile dozens of river rocks on the fire basically smothering it. While those heat up, dig a two foot hole in the ground a little bigger than the animal. Then have a couple of beers. Scoop up the red hot rocks and place a layer the entirety of your pit. Then layer banana leaves about 8 or ten thick on top of the rocks. Add the pig. More banana leaves, another layer of rocks, and then a final layer of leaves sealing in all the heat. Have a few more beers. Open your creation 8-10 hours later! The method of the Solomon Islanders! We ate pretty damn well! The bush oven called a motu... Good mouth watering memories!