Unless you can dig out an earthen pit in the yard, slow inderect heat on the grill is going to be the way to go.
A Boston butt(shoulder) is the optimum cut for this meal. AS far as meat preperation, little can be done, or you can season how ever you want. the hole idea of this dish is the end result. Fork tender, shreadable, lucious pork.
You can easily find banana leaves in any of your local asian grocer, they a usually in the frozen food isle. Thaw what you need, and refreeze the rest, they hold up great. I 'ld score the pork a little to promote even cooking, and allow the seasonings to get in there good. Prep is simple, just bundle your pork in the banana leaves, and secure if needed with some butchers twine.
If you have an out door gas grill, get one side ripping hot, leaving the other side off. Place the pork on the OFF side, and lower the heat on the other side to low. Let it rip for hours....I;ld venture to say 6-8?
I've done this in a charcoal grill. same preperation of meat, but cooking is a little more involved. Get ALOT of charcoal, and secure a burlap bag. Soak the burlap bag in salt water overnight. Start off with about double the coals you think you will need. Get them goin, and let them start to smolder. Once they are all in embers, wring out as much water as possible from your burlap and wrap the pork pbundle in it. Dig a pit in the coals, and burry the bundle. You might want to use a charcoal chimney to have back up embers goin, so you can top it off from time to time. They are available at most home/hardware stores fo 10 bucks or so. Once again, this is going to cook for a looooooooong time...
Hope this will help a little. And don't forget the poi.
Like all good meals, this too shall pass