There are some new insulin meds that don’t need refrigeration. I’d find out about them, see if your son can use them. Try switching and stocking up on the meds. My daughter has gran mal seizures, well controlled with meds. I can’t afford to pay for the name brand(over $300 for a month supply) but, have stocked up on the generic brand($100.00 for 3 month supply).
Another alternative to insulin that doesn’t need refrigeration (especially if it is more expensive than traditional insulin) is to get a super-efficient small frig that can be powered by 1 or 2 solar panels. Just make sure that you get the other equipment you need (deep cycle battery, charge controller, inverter) and that you shield anything electronic from EMP prior to needing it. Here’s one example: http://ecorenovator.org/diy-superefficient-fridge-1-kwh-day/
By the way, getting something like this would save money every single day - which makes money available to stockpile essential food, medicine, etc.