I have found the standard hand winch on the trailer very useful and powerful if run through a pulley attached to the towing bracket thus giving the winch double the power. It could be increased in power by adding further pulleys.
Safety first. Recommend contacting /www.sbstrailers.com/index.php?route=product/category&path=73. New winch to suit. 'Doubling up' especially when using stainless is an accident waiting to happen.