Some people do back heat instead of belly heat. I don't think you should do every other row if you are going with belly heat. You are going to have a huge variation in temps between the rows. My rack is made of melamine and there is no way it would ever transfer enough heat down to provide a correct hot spot.
there is an exotic store that uses heat cord for a rack they have now the snake are very warm but he has the temp going really high but i would run the heat every row
2.3 normals
1.0 100% het pied
1.1 spider
1.0 pastel