Thanks for the explanation of why it is not just polite but safety-critical to clear snow off vehicle roofs! Excellent point!
I agree that actual snow tires are an absolute necessity in snow-country winters, even with that extra weight above the rear axle in your van. Kyle, buy four steel rims, get snows mounted on them, and swap them yourself each fall and spring. Your other tires will last longer (if stored properly) and your overall cost long-term will hardly be any higher.