Nissan Patrol 4x4 (Africa)

bwhahaha.

That amount of grime looks excessive to me. It looks like the interior has never been cleaned properly.

Do as I do, sink it in a water crossing from time to time then to dry it up you dismantle the whole interior, you will find all the dirt then and a great chance to clean it out whilst the rest is drying up.
Take this with a pinch of salt - there are cheaper ways to clean it out ......

Not so funny with insulated carpet flooring however, yours looks like plastic or vinyl covers.