I like where freebeard is going with a single wheel trailer. I'm envisioning a cargo box mounted to a hitch that also improves aero by filling some of that void space in the rear.
I'm guessing someone with a family of 8 isn't willing to custom fab a hitch mounted cargo box, so something off the shelf is likely preferable.
Regarding driving slower, there's no chance I'd consider that with a family of 8. You've got 8 lit fuses there, time is of the essence. Every 1 minute longer it takes to reach a destination is 8 minutes of life consumed.