Since heat rises, back heat isn't the best choice, and you really probably want to keep the room at 80-82 degrees as well, because the heat will not move horizontially to the front of the tub.

Why can't you buy however many feet you need for one shelf and wire each strip, rather than each one foot section? For example - you can get it cut in 3 or 4 foot section if you like, lay it across the shelf and wire just each shelf? Wouldn't that help cut down on the costs? However many shelves is how many connectors you'll need. Make sure your thermostat is rated to handle the total wattage.