tires: the old beetle uses the same size tires. Sometimes when you are looking around it helps to ask for the tires for a early seveties beetle. Anyway 165/65 R15, 185/65 R15, actaually the thinner the better for good snow handling. When i still ran my 120 in the winter i would buy used winter tires, use the phone you will be surprised the deals you can find. Also when it is very cold out the car shifts slowly when the tranny is cold, the first few minutes you have to get the shift just right, and I often skip 2nd as it is too hard to engage, I'm pretty sure this is jsut the oil being very thick at first. As far as oil spray undercoating get whatever is on the market and if you really care about the car and drive it in the winter, give it a good wash underneath next spring and oil spray it again. For undercaoting itself i use wet stick roof repair tar, has about the same consitency as the original product. For hard to reach places I buy a can of the sprayable tar for car underbodies.