I would choose something like this motor speed control which will deliver the torque you need.
, get two , they are cheap for spare parts.
You provide the panel or box and car battery with trickle charger.
https://www.amazon.ca/uniquegoods-C...f=sr_1_19?s=hi&ie=UTF8&qid=1470768763&sr=1-19
You will need a 10A DPDT switch if you want to reverse motor polarity for direction.
** actually a 20A switch or relay for direction using motors if you forget to turn off voltage before changing direction, which is bad form!