Go for it, make sure your brakes are good but you'll be O.K. Everyone seems to forget that probably millions of guys up until 8-10 years ago towed with crappy sup-250HP trucks and everyone survived. Sure it'll be slow and use a bunch of gas but really, heavy trailers aren't some "new" thing people have been towing more weigh with less power for a very very long time. Sure, a 600HP 1000ft-lb diesel would be a better way but it for sure ain't the only way.