Tips for maintaining a third vechile as a tow only

We have had our Sequoia in the garage as a dedicated tow vehicle for 4 years now. We keep up the maintenance, and drive it once per week long enough to get everything up to operating temperatures. We have 4 kids, so finding a 20 mile trip to take it on is no problem at all. As for the cost, since we drive so much, the monthly gas savings between 14 mpg and 32 ( for my Nissan cube ) pays for the payments, maintenance and insurance on the cube.