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I have only done a pit roast (doing one for my wedding too) that was just a pit filled with hot coals and banana leaves (those got expensive..would love to find an alternative) then the pig, more leaves and dirt. Worked great but took a longer time than it was supposed to.

We brined ours as well and also had a few containers of liquid in the pit next to the meat for moisture.

I know those big metal boxes they sell are supposed to work great too (Forgot the name but know they are pricey) but I have only seen them on TV.

Good luck! Fun to experiment.

I recently spit roasted a 150 lb. porker and it took about seven hours all told. My roaster is unique in that the fire is on the side of the meat rather than below. Brine is fine and I recommend it but the trick to deep flavor is constant "painting" with a well seasoned oil based marinade. Don't expect to serve the whole hog at one time. When the time comes, you'll need to shave off the outside layers much like a kebob stand would. Keep spinning, basting and slicing until you're down to the bone.

Lots of information here at ibiblio
http://www.ibiblio.org/lineback/lex.htm

cut and pasted a massive chunk below, but has some helpful charts others might like to see.

also Chef Cosentino posted pretty great info on his blog about his purchase and use of a Caja China to roast a pig for Christmas (I think, it has been a while)

anyway his blog is called "offal good" if you want to search for it.

yep.

Pig pickin' has become a favorite pastime for many North Carolinians. Barbecuing pork on the open grill and serving the delicacy from the grill is known as a pig pickin'. Any month or season of the year is good for pig pickin' in North Carolina.

To have a successful barbecue, the following are some basic instructions for doing the job. Many have some favorite ways to barbecue or have a favorite sauce, but all follow these basic procedures.

Selecting the Carcass
Select a pork carcass that will weigh from 60 to 100 pounds. A live pig weighing 90 to 130 pounds will dress out a carcass approximately the desired weight. The carcass should be lean without too much fat. Excessive fat may cause a flare-up during cooking. The pig should be slaughtered and the carcass properly chilled before cooking. (Editor's note: It is implied, but not explicitly stated, that the carcass should be opened butterfly-fashion for cooking. To do this, saw or cut through the backbone, but not through the meat or skin.) The yield of cooked meat is approximately 35 percent of the carcass weight. Plan on at least 1.5 pounds of carcass weight per person for a generous serving.

Building the Barbecue Pit
The pit should be constructed 12 to 24 inches from the fire to the grill. The advantage of the great distance is for more even heat distribution. An easy way to build a pit is using blocks (8 inch) and laying the blocks two high. Build the pit 3 to 4 feet wide (inside measurements) and as long as needed. Length required normally will take 4 to 5 feet per carcass. Lay metal rods across the cement blocks and place a suitable wire or screen over the rods. Many different types of barbecue pits are used successfully.

Building the Fire
The traditional source of heat is coals from burning oak or hickory wood, however some use charcoal briquettes. If charcoal briquettes are used it will take approximately 60 pounds to cook a 100 pound carcass. Start with 20 pounds of briquettes and allow them to burn outside the pit until gray before spreading in the pit. The heat should be distributed with more heat under the hams and shoulders and less in the center. This will allow the carcass to cook uniformly. Additional briquettes started outside the pit or coals from the hard wood are added to maintain the proper grill temperature as listed below.

Cooking Schedule Approximate Temperature
8:00 am - 12:00 noon Place on grill - cook at 100 - 125 deg F
12:00 - 1:00 pm Cook at 135 - 145 deg F
1:00 - 2:00 pm Cook at 150 - 160 deg F
2:00 - 4:00 pm Cook at 170 - 175 deg F
4:00 pm Turn carcass
4:00 - 4:30 pm Cook at 150 - 160 deg F
4:30 - 6:00 pm Cook at 170 - 200 deg F

Placing Carcass on Grill
Place the pig on the grill lean side down (skin side up) for 4 to 8 hours (depending on weight of carcass), then turn carcass over. Be careful in turning since the carcass may disjoint at this time. Cook with skin side down for an additional 1 to 2 hours. Be sure to use a meat thermometer and get the internal temperature of the hams to 170 deg F to be sure the carcass is completely cooked throughout. Remember, do not cook too fast!

After turning, the carcass can be basted with a sauce of your choosing. A sauce that is usually vinegar, salt, and crushed red pepper -- 2 quarts of vinegar and 1.25 to 1.5 ounces crushed red pepper depending on the degree of hotness desired, and salt to taste. There are many types of barbecue sauces that do an excellent job.

Last, but not least, when you plan a pig pickin' select a congenial group that likes good food and lots of fellowship and you'll have a successful pig pickin'.

Barbecue Sauce
Listed below are ingredients for a tomato catsup sauce for those who desire a tomato flavor.

Ingredients Approximately 6 quarts Approximately 1 quart
Vinegar 2 quarts 2 cups
Worchestershire sauce 4 tbls 1 tbls
Hot pepper sauce 4 tbls 1 tbls
Chili powder 4 tbls 1 tbls
Paprika 8 tbls 2 tbls
Black pepper 12 tbls 3 tbls
Salt 12 tbls 3 tbls
Catsup 3 bottles 3/4 to 1 bottle
Mustard (dry) 3 teas 3/4 teas
Water (optional) 2 cups 1/2 cup

Tom Farmer, Exec. Sec.
N.C. Pork Producers Association

Marketman's in the process of learning how to roast a whole pig...see here:

http://www.marketmanila.com/archives/lechon-round-3-roast-pig-a-la-marketman

I don't really have anything constructive to add to the pig roasting thing (all I know is that my mom or aunt picks up the phone, and MAGICALLY a whole, roasted suckling pig is delivered to our house. It's like we never left the Philippines!)

But, Bunnee, if you ever need a taste tester, I would be happy to volunteer. It's a sacrifice of epic proportions, but I will totally take one for the team.

A whole pig roasted on a spit was without a doubt the most tasty meat I have ever had in my mouth in my life! It was a monster and took all night and a good part of the day, but it was oh, so worth it. The guys made the spit and did all the cooking, but they hired butchers to carve it. Wow, I'll never forget it either.