Getting the Most Storage Out of a Sedan

[Participant]

Any Mustachians have some good tips on squeezing the most space out of a 2012 Civic Sedan in the most cost efficient way? I have a vacation coming up where 5 adults (and our luggage) will be piling in and driving about 1,000 miles. I currently do NOT have a roof rack or tow hitch attached. I do believe this vehicle is rated for a tow hitch, though with minimal weight.

I'm currently leaning towards something like this:
http://www.amazon.com/Rubbermaid-Rooftop-Carrier-13-5-Cubic/dp/B005O0PQ3C/ref=pd_sxp_f_pt
It's a cheap roof mount that doesn't require installing a permanent roof rails.

Anyone have any other suggestions or experience? It's rare that I can''t fit what I need one way or another in my Civic, so a heavy-duty self-made option like MMM made for his hatchback is probably overkill.

[velocistar237]

Could you add a hitch and use something like this:

http://www.harborfreight.com/500-lb-capacity-aluminum-cargo-carrier-92655.html

[GuitarStv]

That luggage holder isn't waterproof . . . so hope for good weather!

Roof mounted stuff tends to suck for gas mileage.  I'd be inclined to get a hitch and small trailer if you think that you would use it at all.  Having a hitch is really handy for moving stuff . . . bikes, construction supplies, luggage for trips, the occasional appliance, etc.)

[Participant]

Thank you for the feedback. I looked at hitches. They do seem like the most rugged and fuel efficient way to go.

That said, they seem to cost about $150 without installation. The small carriers that attach to them are another $50-$90. Then I would still need a waterproof bag or tarp. If was planning on using this even semi-occasionally, i would probably go with that, but since this I've had this car for two years and this is the first time this has come up, I just don't think a hitch would get enough use to be worth it.

Unless there's a cheaper hitch (or similar product) out there somewhere that I'm missing.