We made the mistake of spreading out 2" of sea shells (we live in FL), 4 years later we have CRUSHED sea shells. We are thinking of replacing the shells with 2" stones, they hold up better. We also put the weed guard screen under the shells, that has worked great for keeping the weeds out. As long as you do not have grass or weeds under the TT, there is no need for a ground tarp, the bottom of the TT is high enough above the ground so it doesn't trap moisture under it like a car does.
If you can do concrete, that is the way to go.
2013 Jayco Eagle 284BHS
250Watt Grape Solar Panel, MorningStar MPPT 60 Charge Controller
1500 Watt Ramsond PSI, 2 Trojan T145 Batteries (260Ah)
2 - AirSight Wireless IP Cameras (used as rear view cameras)
EnGenius WI-FI extender, D-Link wireless (n) modem
MagicJack Internet Phone
2012 Ford F150XLT, EcoBoost w/3.73
157" Wheel base, HD Towing Package
Our Solar Album http://www.jaycoowners.com/album.php?albumid=329