Remix of the idea thing:2253801 Very little variation to adapt it to the 5V "35W" solar panel. And direct connection to the watertight box. I've rotated the axis for horizontal cell orientation.

Box 100x100x70mm-4 https://es.aliexpress.com/item/1005007205133595.html?gatewayAdapt=glo2esp

CN3791 MPPT 6V https://es.aliexpress.com/item/1005007355378997.html?gatewayAdapt=glo2esp

Sunpower 35W Portable Solar Panel 5V Solar Panel https://es.aliexpress.com/item/1005007701773816.html?gatewayAdapt=glo2esp