Never purchased one (for the season) but I have sat in them and they are comfortable. No they do not remove them all year but as long as you have a towel I don't believe they take in water...
Solution solved: Pocket ponchos...usually less than $1...at Walmart/Target (camping area or large bin by registers), as we always take them to every game...never know when you will need them (rain, something spills on bench/seat, etc...). If you didn't need it, take it out of your pocket and save for next time.