Shall I cover my travel trailer during winter time?

I always cover.Tried the commercial covers but they allow water or melted snow through and camper was always dirty when you removed the cover.Plus,they were expensive and only last a few years.For the past 5 years or so I have used a 30 x 20ft plastic tarp and cover with that.I also bought 2 " webing at the hardware store with buckles and run them over the top of trap and under RV.Then tie the ends with rope. The tarps are about $60 and last one or 2 years but when I uncover the unit it is clean.