Clear Silicone seal does wonders when it comes to weatherproofing and sealing against moisture. I used it to cover up and protect the Joule Thief parts on this nearly disposable flashlight.
Components I wound two six inch lengths of 20 AWG (0.25mm) solid enameled magnet wire (bifilar wound) onto a 0.25 inch outside diameter ferrite toroid. This core was a T231212T from Surplussales.com. They were about $.25 (US) apiece.
The transistor was an everyday, common PN2222A, often mistakenly called a 2N2222A. The resistor was the standard 1000 ohm or 1k, 5%, 1/4 watt resistor.
I inserted a AAA cell to make sure it was working properly and then I covered the whole circuit with clear silicone seal, to protect the components and waterproof them, and set it aside to dry. A few hours later I had my nearly disposable Joule Thief flashlight.
I didn’t use an on/off switch; I decided the user could use a piece of paper folded in half between the contacts to turn it off. Or else, just remove the AAA cell. Most of the cost was in the battery holder, which was about a dollar.