> I was thinking about hanging a space blanket liner inside but am pretty sure
> condensation would make that a bad plan.

Yeah, if we pull the space blanket over our heads in the winter, our breath condenses so much moisture on the underside of the space blanket that it soaks our bags. Those blankets are impervious to moisture. Same with your tarp - if it's outside your tent, be sure there's a gap so the tent can breathe and not have the moisture collect on the underside of the tarp. If the tarp's in contact with the tent, condensation will wick through there. I've had that happen in a rain storm. Not fun.

Our tent:

The tent and fly are integral. You run the poles through, and the whole thing is set up in one swell foop. Makes it hard to clean, though, after a week at Burning Man.