Any advice on the Bolt as a back-up?
If you're thinking of an SB, a VERY smart move BTW, save your money and skip the Bolt. Buy a few more batteries with it.
Better yet, spend $40 more and just get another SB. The Bolt has had issues with internal wire breakage. This may, or may not, be relatively easy to repair, depending on your skills and equipment but the SB has never had ANY issues with reliability. Ever.
The chances of a SB breaking down are about the same as the chances that all your juice will spontaneously explode.
Personally, I would never go far from civilization relying on eGo batteries. Only an SB, or a full mechanical mod, is good enough.
I have a BB, a smaller version of the SB. It's been run over by a truck, dumped in saltwater, buried in mud and dropped from various moving vehicles. It still works fine. The SB is even more reliable and robust.
If you are going to be in an area with spotty electrical service, maximize the number of batteries and charge as many of them as possible all at once. A solar charger may be good, depending on how many hours of strong sunlight you can get, but they are slow and jungles are no known for strong sunlight. I'd rather have 3-4 hours a day of electricity to charge 4 batteries at a time than 12 hours of weak sunlight and a solar charger. Solar is for those situations where nothing else is possible. The tiniest generator and a gallon of fuel would be preferable, as long as you have the space for it.
I have been in a similar situation for a couple weeks at a time on a boat with no electricity. In that situation, a solar charger worked to charge 2 batteries at a time, but it still took a looooong time, even with a lot of strong sunlight.
A lot of this depends on the portability/size/noise factor. A solar charger would be o.k. if it was large and you used it to charge up a bank of SLA batteries. Then, you could charge off 12V and wouldn't need strong, consistent sunlight. But that could be as bulky as a generator.