The cargo area in the LR3 looks bigger than in my D2, but it feels so limiting. I'm constantly trying to find more room. I'm thinking the only solution for road trips is a roof rack or roof cargo box. A roof rack is a pretty big commitment unless you go "nwoods-style" and install quick disconnects on the rack for an easy up and down. A roof rack with an all-weather cargo bag to protect your luggage from the elements would be great and you can even use the rack to carry accessories.
A roof box/pod from Thule or Yakima would be the most realistic method for on-road road trips. When you're not using it just remove it and store it.
2006 LR3 SE7 w/HD Pkg & 285/60 Nitto Terra Grapplers