Given the conditions that you stated, 5 rainy commutes a year is all, I agree with the majority that a cover is not needed. If you are going touring, though, you may be talking about major wetness and for that, to me, it would make sense to protect your leather saddle from the wetness. I have always slathered Sno-Seal on the underside of the seat and had a good sturdy full coverage soft plastic cover for rainy days and overnight.