Cooking in an Electric Roaster?

I am having around 20-30 people over for my son's birthday. I am making Ham and Scalloped Potatoes and just purchased an 18 Quart electric roaster so that I can triple my recipe. My question is, does anyone know if they cook the same as an oven? How should I adjust my cooking time. My original recipe is 350 and covered for first 1/2 hour and uncovered for last hour/hour 1/2. Can I bake with the roaster not covered? Thanks for any help!