Those tub dimensions sound pretty good. My adult colubrids are housed in 32 qt tubs, my yearling/med snakes/young larger snakes in 15 qt tubs, and my smaller babies in 6 qt tubs. Hatchlings stay in Ziploc sandwich-sized tupperware containers until they are large enough to move to 6qt tubs.
I don't use a separate heating system for most of my racks, as I live in Arizona and have enough problems keeping ambient temps down for the most part. Any young larger snakes (ie boas, BPs, Burms, Retics, etc) that are housed in the 15qt bins have their own rack that does have heat. Other than that, I let my ambient temps do the work. During the winter, I use a small space heater to help keep the temps maintained and in the summer I often have to open my vent to allow cooling. Ambient temps in my reptile room range between 76-84, which are perfect for most of my colubrids. I have a few that take up refuge in a certain "cool" corner of the reptile room, as their temp requirements are a bit cooler than that.
Since you live in VA, I would suggest looking for a rack system with heat. Temps are easy for me... I live in a desert, and my animals thrive at my temps. With how cold it can get there, I would look into a pre-wired rack. Animal Plastics has the least expensive "Economy" rack that I believe is only about $175 with heat. These racks accommodate the 32qt bins (1 per level) or the 15qt bins (2 side-by-side). They can be made with as many levels as you need. You could possibly get away with stacking them, but one can find many faults in the security of just a plain bin and lid combo, especially with a snake as small as your Herald's. For security reasons, a rack would be the best choice as well.