I generally just cook over open coals, but then if there's a bunch of people and there will be a reason to have them "available" all afternoon, I'm a big proponent of "The Brat Tub" (yes, it rhymes with Hot Tub, people.....please don't pronounce the sausage like a spoiled child).btw, those brats look great! do you cook 'em in beer?
Saute some onions in butter (or olive oil) in a pot large enough to hold all your brats and then a enough beer to completely submerge all your brats. After the brats are done, they can sit in the brat tub all afternoon (it's like a delicious steam table for your sausage friends). Don't forge to add some of those delicious onions when your;e serving up your brat.