i havent had the chance yet but i dont see why there would be any problem, if i can manage to drive a 240sx with well over 400hp at the rear wheels with completely bald tires and only 2 front seats, doorpanels, and a dashboard in winter all year last year without any problems i dont see why it would be such a hard time to drive a mustang with tons less hp and alot more weight to it, not to mention tread on the tires LOL
but if your worried about it go to your hardware store buy some sand bags, go to the tire shop and get some studded rear tires, and just taker easy on the gas and brakes
but be careful if your gunna put weight in the back, cause if you put too much you will loose traction in the front and yes yo may be able to go straight but good luck turning, lol, my suggestion is to throw a max of 50pounds back there ( 1 10in sub and box works perfect) and call it good. | 
