They make receiver-type hitches for almost anything (even my humble little 2000 Saturn Wagon) ... they bolt to the under-body through the floor with some inside straps to distribute the load ... pretty easy to install. Google TailerHitch.com or similar and do a search for your make & model ... it'll be there!
Believe it or not, my Saturn SL2 is rated to tow 2,000# with a 200# tongue weight (and I have!), so your Focus is probably rated at 1,000# with a 100# tongue weight ... you shouldn't have any problem putting your gear inside the TD and being able to pull it.
Go for it, Dude ... and get out & go camping ...


CHEERS!