Carl...New cars are not stored indoors for long periods of time. They are designed to spend all their lives out in the elements so whats the need? Yours (your Mums) will have sat outside on a parking lot in the open from the day it was delivered to the dealer until your Mum bought it and it was taken inside to be prepped. The salesman will tell you it was under cover for 3 reasons.
1) People dont like the idea of it being stored outside in the open.
2) Its what you want to hear and.........
3) Because he thinks you are gulliable enough to believe him.