Just got back from a trip to NM in my wife's new Subaru Outback. It is a nice car for a road trip. We got about 26MPG for the whole trip...not bad for being in the mountains most of the time. I don;t know how it would do pulling a trailer but I sure it would do better than 13mpg.
I have a 2012 outback, worst I have ever got in mileage was 20.5 with two big kayaks going south to the coast into a 25 mph wind with 40 mph gusts, usually get 27-28 with two kayaks on top haven't run a trailer on it yet but supposedly with the light weight trailers it gets normal mileage. I am 5'11" and cant sleep in it with the seats folded. I have looked at some of the smaller a-frame pop ups that sleep two with AC available and with the flat 4 it will tow 2800 lbs. Also looking at a Space Trailer for a little more than the rack n roll that can be used for a utility trailer with the top off.
To the OP I got rid of my tundra for that same reason gas mileage was not so good, switched to an FJ Cruiser and it was not much better then got the Subaru and have not looked back. If I drive gently I get 26 in town and have gotten over the epa rating of 29 miles per gallon highway on many occasions. The new ones are rated for higher and have about the same towing capability.