Nick
If you are only after tracking and you own an Argo Navis you can't go past the Servocat- they make a model to fit Meade 16" ( It can be adapted to other similar dobsonians only USD $1099) . It will have the advantage of scope not tilting over as it tracks and also will GOTO.
http://www.stellarcat.com/Pages/servocatjr.html