I have the yakima skybox21 the big one i also have 78inch cross bars that connect to the factory rails on my 2010 suburban. I use the box regularly, im 5'6 and i can put the box on/off the roof myself in about 10 minute. I went with 78 bars with option of using a second box. On one ski trip 6 hours away we had my box and my buddies thule box on there. His box was smaller so had skis/boards/poles for 5 people, my box had all the clothing bags and we loaded the back of the truck with food / coolers.
Last year on a 15000km trip across canada, down pacific coast into nevada/utah/co i had the box on. I would use the box for storage of gear we werent immediatly using example, in BC we wemt to Whistler when we qere in Utah we didnt need ski/boards so they were in the box. The truck was jammed with gear and still avg 11l/100kms.
My plan is to get some type of rack (gobi or similar) and still use the box. I have 2 dogs who each travel in an airline crate in the back so cargo space is reduced. I currently mount the box on the right half of the roof bars mainly because i have 3 uhf/vhf antennas drilled thru the middle of the roof. So if i mount the box to the right half of a gobi-style i would still have room to tie down stuff. As previously mentioned, they are well sealed from environment (4 day wind/sand storm in Moab, not much got into the box, yet i still find red sand daily inside the truck). And yes i though of sleeping in it during this sand/wind storm after getting tired of waking up with an inch of sand in the tent. Ended up sleeping in the suburban
Anyways thats my story!
Nic