The stoutest plastic I have yet encountered is colored gray (Grey for BLT13).
They gray is not shiny. Rather fibers (fibres for BLT) can be seen running helter skelter throughout. Tool boxes, cargo boxes, and other plastic items have been made from it and they are damned near indestructible.
As was mentioned above I heartily endorse gobbing dielectric silicone GREASE all over the seven studs inside, over the wire jacketing where cables pass through rubber grommets.
Use ADEL rubber/steel cable clamps 2" from the box to support the cables. Clever mechanics will go online and purchase ready-to-go 12 volt LED 5mm lights and bezels and drill 7 holes in the lid for the lamps. Presto! A diagnostic tool-in-place. Over the years you will not believe how much time the LED modification will save.
(I hope BFL13 is in a good mood today :) )