some additional thoughts, I'll try not to repeat, hyou've gotten a lot of good advice already.
go soft sided. mine folds up into approx. 12x12x6 inch cube (back in original zip up bag) and fits nicely into luggage if you are only flying one way or renting car and changing locations mid flight.
we too are family of 6/7/8 (don't ask!)and drive an extended length aerostar(huge amount of storage) but with that many kids and strollers, car seats, etc. . .it is so nice to have room for feet and legs inside van.
I do not have a tall husband (5'8") and he truly does grouch everytime he has to put it up or get it down. says it's a half hour exercise to make one want to simplify their life! that said, he's quit complaining since he like a nice neat organized van to travel in better than stuff exploding everywhere!
my soft sided carrier held 5 medium rolling suitcases and a misc. bag. some are longer and less wide dimension wise, some are squarer, read the dimensions and know what you want to put in it.
been through rain, snow, and ice storms and even though I wrap in black trash bags each time, nothing has ever been the slighest bit wet.
best news yet. we've borrowed one (high quality from a friend~ didn't like zipper thingy) purchased two (cheapies!! one from
Walmart and one from auto store Pep Boys~ both $20 a piece) Pep boys one had better dimensions but also got small rip on first use (bum) but at that price I guess I could just consider it disposable! I didn't though, I returned it and said I thought it shouldn't have done that and they offered me a new one or a complete refund, works for me.
caution: we travel to cities a lot, watch out, it won't usually fit in a parking garage on top of a high van, might be okay on a car or lower van. because it is so high up and so well belted down I can't imagine anyone trying to steal it!
ideally, we'd all own huge SUV's or 8 passanger vans with all gas included !