Spray the inside of your slow cooker with non-stick spray.
Add in 2 jars of Alfredo sauce. I like to put 1/4-1/2 C milk or wine into each jar and swill it around to get the sauce that sticks to the glass out. The wine gives it a more grown-up taste. Let heat on low for 2 hours. ( If you're like me, there's no such thing as "too much garlic", so if you like garlic, you'll want to add it now to cook into & mellow out with the sauce.) If using fresh or frozen veggies, add them now.
After 2 hours from the start time, add uncooked seafood, if that's what you are using. This is the fun part. You can vary it up, Use clams, your favorite mild fish cut into bite sized pieces, scallops, etc alone or in any combination. (Since the shrimp & Krab are cooked, they only take about an hour to heat through.) If using canned veggies, add them now.
After 3 hrs from the start time, If using small pre-cooked shrimp and imitation Krab, add it now, as it just needs to heat through. This is also when you add your cooked and drained pasta, stir it into the sauce and let it heat through the last hour. The pasta will absorb most of the sauce.
Variation: I you like your sauce separate from your pasta, finish cooking the sauce and seafood. When the 4 hrs are nearly done, cook and drain your pasta, then just serve your sauce over the pasta. Also, you don't HAVE to use veggies. I just found it a good way to sneak them in when my kids were little.