Under tank heater?

I am going to make another enclosure out of a 27qt shallow Sterilite container is it ok to put a Zoomed under tank heater with it or will it melt the plastic.

It will be fine. I had the same question, but have now tried heat pads and UTH under Sterilite plastic with no problem.

Ok cool will my other tank be ok with just the basking light.

I can't recommend just a basking light with ball pythons because they do need belly heat (which the light may or may not provide enough of), lights tend to dry out an enclosure, and unless it's a non-visible spectrum light for bp's (UV, blacklight, etc.) it needs to be off at night for proper photo periods. You can try it, especially if the light type isn't a problem, but I'd think it worth the cost an effort to run up to your nearest drug store or Wal-Mart and spend $10 or $15 on a heat pad for humans with adjustable temperature and no auto-shutoff.

Heat pads work well enough. But for rubbermaids I reccomend a radiant heat panel. It's like a heat pad you place on the top of your cage. And it radiated heat down like a lamp.