I think it will all depend on how noisy your base location is. I know that my car, other cars, some traffic signals, parking lot lights... cause noise in my receive. if you don't have anything causing noise in your general vicinity - blenders, microwaves, hair driers, a noisy power supply, etc... - you'll be great.
no idea if the above listed do cause noise, just pointing out possibilities.
when I go out to my folks house, 20 miles from somewhere, it's nice and quiet with the car off.
my base antenna will be up in a month, if you want to wait I can give you my opinion then. as of now, mine has never left the mobile.