I agree with the others about security being the number one reason your snake isn't eating. If you haven't yet you need to cover the sides and back with at the very least paper. But you can also use Styrofoam, or R-21 insulation.(Lowes or Home Depot) R 21 insulates really, really well (better than Styrofoam) and can be cut with a scissors. You can put the R-21 or Styrofoam over the paper even.
Sounds like you have got the uth and it's temp right. You can get the black hides from ReptileBasics dot com and even Amazon sells small black hides by Pangea for 8 dollars a hide )small. 8.50 for medium.
My next question is how is your ambient temp. A low ambient temp can cause a snake to quit eating. I like to have mine up around 80 or 82(even better) Can you use a dome and night bulb (Zilla black light)-Petco or che on a thermostat to help keep the ambient heat in the low 80's Amazon sell thermostats as well. As far as cheaper but lesser dependability than say a Herpstat go you can buy a Vivosun. There a LOTS of low end thermostats. The best high end thermostat is Herpstat which costs more but is high quality. and there is also the VE which reptilebasics sells which is good quality as well.
The VE 300 which sells for a decent price on Reptile Basics runs 3 devices which might be good if you end up using that larger front open tank you pictured but that will need to be way down the road once your snake is eating and a lot bigger. But you could still get the ve-300 now. And run your uth and a heat bulb or che. with it. plus one other device.
And I agree with Moose after you get the security and (maybe) ambient temp straighten out you should get you a live mouse from Petco or another store. There I said it. That store (Petco) sells live feeders and other local pet stores do too. God Bless Em. And I think it is more cruel to starve a snake or any animal then to have a mouse die in less than a minute in the way nature has worked out. Not too many snakes getting frozen thawed feeders delivered to them in the out doors. In the US or Africa, South America, or anywhere else for that matter.