Like the bass drum, it is worth practicing the 12 positions for notes within a bar of triplets on the snare drum. First you should go through the 12 positions in the manner of example 74 and then try example 77 which uses combinations of the 12 positions. Take it slowly and count out loud as you play, accenting the snare drum hits with your voice.
Once you can do this exercise, try swapping the snare drum part to the right foot, then the right hand, then the left foot to help you develop good independence when using triplets. When you can do this, improvise triplet based rhythms with one limb at a time while keeping the basic beat with the other three limbs.