The most effective protection is usually done with conventional diodes from the motor terminals to power and ground. The forward surge current spec of the diodes is the spec to pay attention to. You will find a much smaller diode than you would expect is effective and reliable.

I'm a IVP guy so don't have a wiring diagram for your bird. If you choose to forward your relay schematic to me, I would be happy to confirm the above approach. I suspect others on the list already are using the diode solution. In any case I would try and stay away from the suppressor approach since it is more prone to failure especially from improper "jump start" procedures.

Hope this helps,

Jack Morgan