Is it possible to waterproof my charger(s)

Amazon has a box that is perfect for waterproofing 1 to 4 chargers.

https://www.amazon.com/gp/product/B009RX5H6S/

The medium box can hold 1 - 2 chargers.  The large box can hold 1 to 4 chargers. The small box is too small for a single charger.

You can use this 4 way splitter to power your chargers

https://www.amazon.com/gp/product/B01IRIQSY8/

Here are pictures: