If you don't have a rack yet, you might also consider the 1-up roof mount rack. They're top of the line racks and will fit the Oliver rack without any modification apart from drilling the holes to secure it. Just order the flush mount kit and it should work fine. Their racks run $189 each, so for two they're comparable to the Thule. They sell a fat bike conversion spacer for $34, and since they're two separate racks, you can space them apart however far you want.