I use this for long trips in my Samurai. I have never used it for firewood but the material is thick and it has kept things perfectly dry for thousands of miles on top of my roof rack. No issues at all with dust or rain getting in...
I am planning on running the 2" ball on my off road trailer and looking into making my own max coupler style setup for the times I really need it. I agree that most of the time for me the 2" ball will be just fine since any extreme rock crawler would have the trailer left at camp