If you are only going to experience this scenario once or twice, build the rear for your desired usage. You don't want to rebuild your rear end several times to switch from haul
ing to haul
er. The taller gears will give you better performance, but decreased gas mileage (your tires will turn faster, resulting in higher RPMs at the same speed). I switched from 3.27s to 4.10s and the increased performance versus the slight decrease in gas efficency (highway cruising mostly) was worth it. Here is a website that you can play with and see the differences....
http://www.svtoa-atlanta.org/cgi-bin/trans.cgi
Also look into renting a truck/suv/van with a hitch installed if you can swing it. It will keep that stress off your Stang.