This site gives the straight up info on a 10 gallon cream can dinner, which feeds 30+:

barbequelovers.com/grills/milk-can-dinners/cream-can-dinner-recipe

This is what they say for sausage for about 30:
about 10 lbs of sausage (brats, german sausage, smoked sausage, Italian sausage, etc.) Mix it up. Don’t just use one kind and don’t be afraid to add at least some spicy sausage as it will add some nice flavor. It is not absolutely necessary to cook the sausage before adding to the can, but we find it does taste better if you grill it beforehand (if it is not already cooked when you buy the package). We recommend the Johnsonville Sweet Italian brats, especially if you grill ‘em first. Cut all sausage in about thirds after cooking. Also especially tasty are Hillshire Farms hot and spicy Italian Sausage.

This is a VERY good instruction, use it for your basic info, even with a roaster.

To adapt for a roaster, this is what I would do:

1) An 18-20 quart roaster is the equivalent of a 4 1/2 gallon can, so plan on at most 1/2 the amounts, feeding about 16.

2) Nesco roasters have the heating element in the sides, which is NOT the best for this recipe. One with the element on the bottom, such as the Hamilton Beach, is what you want.

2) Put a heavy rack in the bottom of the roaster that covers the whole bottom. You want the liquid to sit under the food, not the food sitting in the liquid. You can measure how much liquid to add by setting this up. putting in water up to the rack, then measuring the water. You will replace the water with your steaming liquid (beer or broth) when you do the recipe.

3) If you have any doubts about the depth of the rack, put the corn in the bottom layer to lift up the other food.

4) Layer in the food as discussed in the recipe, meats on top. One potato where you can poke it to check doneness. Then the future steaming liquid.

5) Put the lid on, and then leave it on until the cooking is done and it has sat the required 5 plus minutes after.

6) Turn on to 325-350.

7) Start timing only from when steam comes out the vent hole. 30 minutes at least- can be much longer. Turn off, let sit 5+ minutes.

8) Open and enjoy. Don't put the food on trash bags as suggested in some recipes; trash bags are NOT food safe plastic.

barbequelovers.com/recipes/milk-can-dinner-food-for-40

www.instructables.com/id/Cream-Can-Cooking/

Here are some of their notes:

This needs to be done when corn is in season
For a 10 Gal can: 2" of liquid to start = 1 1/2 gal. I started with 4 cans of beer and then the rest of the 1 1/2 gal. liquid was water. The cabbage on the bottom of the can takes any "burn" that might happen. My guests wanted more cabbage and I had a total of 6 heads....quartered, four on the bottom and two on top.Next time I'll add more cabbage I guess!!! :-) see below
Break the corn cobs into halves for easier handling when turning out and for the guests use also
If you use small pre-packaged pre-peeled carrots they cook too fast and break down. I used 5 lbs of bulk carrots and could have used more. They were cut into approx. 5-6" lengths
Pour off all the liquid (retain some) before you turn your prepared food into bowls. It not only keeps from splashing hot liquid but it's easier to separate the individual product into containers, all corn, all brats, all potatoes, etc. Also, food does not continue to cook when out of the hot liquid
Try and buy potatoes all the same size so they will cook evenly
I put in 50 brats and 2 large ham shanks (quartered). The ham shanks were plenty of seasoning so I didn't have to salt and pepper. Some people salt and pepper before they even taste the food anyway. I figured I'd let them do that but it didn't appear that too many did. The ham shanks were in demand and I may use more of them at a later time. As the brats are close to the top, I could spear one after 1 1/2 hours of cooking on the propane burner and determine if all was done and ready