Belly Heat or Back heat

I breeder consolidating in my area has a large 9-bin rack for sale. but it is belly heat. I was gonna put my three big breeders in the top three then put their babies in smaller tubs that would fit inside of the big tub that goes with the rack.. I was told belly heat is bad for babies. It does have a Herpstat II with it...... what are your thoughts on belly heat and is there a place to go for easy to read instructions to make my own rack that doesn't require a rocket scientist to build.

belly heat is not bad for any ball python. back heat might be preferable when they're young, but I would be more concerned with the proper tub size than heat source.

as for the DIY racks, check the forum. there are a number of good build options detailed there. I can't recall who authored the thread offhand but 'the frugal herper's snake rack' post is a great place to start.

if the tub maintains the temps your going for, then it doesn't matter.

personally I do everything 100% back heat, works best for me with, my rack design, in my house, in the climate I live in.

Back heat is only bad for hatchlings because of the size of tubs used.
It's more difficult to achieve the proper temperature gradient in the small 6 quart hatchling tub, so that is why back heat is preferred there. With belly heat, heating up a 6 qt tub can mean just a hot spot and no 'cool side'.
If you were to use a larger tub (i.e. 12-15qts), using belly heat is possible. But I believe the 6 qt tubs can be used if you don't put the tub over the flexwatt all the way. It really depends.

Personally, I use belly heat for my snakes. I really like back heat, but it didn't work out well in my house.
I have a room temp of 70-75 degrees. When using back heat, the flexwatt was 120 degrees to achieve a 90 degree hot spot in the tubs. That's because back heat heats up the air rather than creates a specific hot spot like belly heat.
Flexwatt isn't designed to run over 100 degrees so I was rather uncomfortable with it running 120. I switched over to belly heat and in the same room, the flexwatt only had to run about 98 to achieve a 90 degree hot spot.

It really depends on how warm your room temperature is. If your room is 80+, back heat works well. Anything lower, it doesn't work very efficiently.