Nothing in the ST category is going to give you service similar to an LT tire. Maxxis is a good ST tire but they still need replacing after 4-5 years regardless of mileage.
I use Maxxis tires on our nearly 10K# TT TH and tow under the same conditions you outlined and from my experience they do provide better service than most of the current crop of ST tires.
Your best bet if you have the room is to go to an LT tire for the peace of mind that no ST tire can provide. I haven't had any blowouts with our Maxxis ST tires but I don't expect them to go longer than 5 years.