Ok lets see here,
If you want to do a camo job, red brown thick lines or medium sized blotches would probably work. The interior would be German Gary. Figures, A dml figure for the driver will work even if he's not Africa korps. for the men in the back, just search around on the internet and you'll find figs you like, just be sure they have north africa clothing.
Submerging the vehicle will be something different. Ive never done it, but cutting it seems like it would work. Or just make the water deep and cover it up.
bridge, you can buy one via Verlinden (nice looking one at that) Or you can build your own from balsa or another type of wood that is close to scale.
Dont use the sand, or the dirt. Use a product called Celluclay. Mix it with the proper color paint (just cheap craft paint) and then apply. Then just add som railroad ballast and kitty litter (the plain kind) for rocks, then some slight vegitation. Well your by a river so, maybe a bit heavier vegitation.