When I had my 14ft TT, I would bring a 4 person instant tent and use it as an outbuilding. No one ever messed with my stuff and it was nice to have it out of sight. I would just set it up behind the TT. The TT and the 8ft tent combined still had me under the length of most other rigs.
I upgraded to an 18ft this year, and used the bunks for storage for the two weekend trips we were able to squeeze in. But, for longer trips I will bring the tent as long as the campground allows two "dwellings". It is handy for keeping chairs and gear out of the weather and takes little time to set up. And, it gives my introverted self an extra room.
-Laura 2016 Shasta Oasis 18BH & 2015 Ram 1500 Hemi