Just about any well made tranny cooler kit with an integrated fan will work. Obviously there are poorer quality ones but most are just fine.
All I would do is Make damn sure that a rock can't pierce it, and that there is a heat sensitive valve that allows the tranny to heat up properly before the cooler is engaged (which is probably a non issue in California but..)
You already have lines that run up to the radiator from the trans, why not add the cooler up front No adding a fan (more maintenance) with constant clear air flow. Cooler on the left is the trans cooler, right is PS cooler