I own a rival crockpot bbq pit, which states that a low temp it is 230 f..high is 280 f...I want to cook a whole 20 lb turkey in it for thanksgiving ..can't seem to find lengh of time to cook the bird..if you could help I would be thankful..for stuffed and unstuffed..

Hi Pamela, great question. I haven't used the bbq pits so I don't know for sure, but if the lid fits on the pot completely, I would use it just like a large slow cooker. The temps you listed sound about right --- so if it was me, I'd plan on cooking a fully-thawed unstuffed 20 pound bird for 8 hours on low, 5 to 6 on high, and check the internal temperature with a meat thermometer to ensure doneness. Since it's Thanksgiving -- you'll be home to check the temp. I'd suggest checking it after 5 hours on low or 3 on high to see how it's going. It's okay to take the lid off near the end of cooking time, but I wouldn't fuss with it the first few hours.
Now if the lid doesn't fit all the way on, you'll need to make sure that it's pretty well sealed with lots and lots of foil.
good luck! It's going to work --- the bird may fall apart a bit but it'll cook just great and since the lid is on it'll sort of self-baste and make a beautifully juicy meat!!