ok made a start on the concepting while its quiet here at work, forgive the colouring, done with a mouse.
right just check the coast is clear.
heres the concept for the level.

the wwo platforms at each end are the start/spawn points.
think i might add more levels of ground at each end, probably sloping up towards each base to add a little advantage to the defending side.
heres a concept of the tanks

the idea for the top left hand tank is that each section is a panel that can be hit damaging the tank. a bit like a target, even thought about colouring it like one.
each half of the outer ring corresponds to the tracks, the more sections damaged the slower you turn in each direction, until you cant move no more when they are all hit, or if you only have one side you can only spin.
the 4 sections on the gun correspond to gun reload speed, slowing with more section gone until, you can no longer fire and have to try for a draw by holding out(running away)
the top (nipple) is where the driver sits and is there for the bullseye. one hit and your out.
heres some concepts for the vegetation, yay giant mushrooms.

the mushrooms are going to have simple damage models with the top gone so they nolonger provide cover.
another idea i had is Puff balls, remember chucking those at people they explode in clouds of spores. they could either provide means for escape (Small cloud of dust) if the DS is up to it??? or behave like a barrel of explosives in so many games creating an area of damahge.