Update
Current fuel economy numbers: the Foz has done better than expected in the economy department, even with a roof tent it's been able to hold on to 20s. The tent seems to make little or no difference at lower speeds. All measurements are with the 35mm lift kit and oversize 215/70R16 Yokohama Geolandars.
With roof tent:
~22 highway (cruising at 75mph)
~22.5 during "spirited" mountain driving (aka, tires squeeling around the corners :smiley_drive: )
~21 on a daily city commute of 3.5 miles
Without roof tent:
~25 highway (cruising at 75mph)
~23.5 "spirited" mountain driving
~21 city commute
Trail use tends to be about the same as "spirited mountain driving" on a vehicle like this. Low speed crawling is tough to measure since we haven't run into many spots requiring low speeds that are long enough to get a measurement.
The roof tent was a fun diversion, but a bit outside the scope of a light/economical adventurer so we've pulled it off in favor of cargo space (bikes, canoe, etc). With capability sorted, it's time to look at protection with full underbody armor, cargo handling, and a few convenience items. Details to come...
The tent is now for sale here:
http://www.expeditionportal.com/forum/threads/118981-FS-Ultralight-Rooftent-on-a-Budget-500-OBO