Bass solution for my kid...

Hi all,
Been out of the car audio scene for about 20 years so I need a little advice. Would like to get my daughter a sub + amp for her 2010 Subaru Outback. I would like to keep it as simple as possible. Something she could move or take out in case she needs the trunk space and so.ething that could be added to her existing stock stereo. I thought about something like a 10" Bazooka bass tube or something similar as it would be easy to move or remove. Like I said, been out of the game for a while so just looking for suggestions. Thanks.
Paul