I would guess you've got past this by now.  But if not, I may have the help you need.  Also, others may benefit.   I've done some of my own searching for walk through help and find that it all stinks.  Most of the walk through stuff lamely shows you the map and tells you to kill everything without providing sufficient detail. 

I just got by this map on the hardest skill setting and it was not easy.   My case was made more difficult since on the first try (before i even knew there was a tank or infinite respawning Higs), I died just as Rico was dashing around the corner where the tank and all the Higs are waiting.  I had a Bolt with only 8 shots left at the time.  Since Rico was rounding the corner - no stopping - this made it very hard for me.  On each of my subsequent respawns, I was stuck with that Bolt with 8 shots.  I couldn't go backwards and get a better suited weapon without him getting killed.  Sucked. 

Anyway...

Keep in mind, you will NOT pass the checkpoint until you're inside the engine room!   If you die at any point prior to that you will have to start this portion all over.  When you round the corner where the tank first comes into view, there are two spots for cover in the middle.  Advance to the first one while firing at a large group of Higs on your right.  Reload when you get behind cover.  You may then have to shoot left or right depending on where Rico goes and how effective he is.  God this part made me hate Rico.   I shot him myself a few time just out of anger.  Once you and Rico kill this first wave, advance behind the next spot for cover, which is the gun rack where the Missile launcher is.  Get the missile launcher and fire at the tank.  You should have time to reload and fire again before the next wave of Higs will be upon you.   Success depends on this.   Step out from behind the gun rack to your left and shoot the missile.  Then back behind the rack for cover.  Watch out for inbound missiles.   It is possible to knock out the tank with two shots.   Just be sure to hit it in the middle just below the turret.   Once the tank is knocked out, you may need to use one more missle to kill approaching Higs.  I found this useful since it is hard to switch back to a different weapon with them approaching quickly.   But it is important not to use up all your missles.  Be sure to save 2.  Note that to the left of the gun rack, across the ailse so to speak, is a 3-pack of missles. 

Once the tank is blown, the Higs will cease respawning.  Mop up any resistance with a sub-machine gun, etc.  Once they're all dead, equip the missile launcher again and advance towards the engine to the rectangular box - it's in the center of the train.   As you near the end of this box, Higs will come out of two upstairs doors, on the left and right .  Use the missile launcher to take out the Higs shooting missles at you .  I found that they tend to aim high so it's easier to dodge by moving forward a bit.   Now switch to your pistol (so you can run faster) and retreat all the way back to the ammo rack after taking out the Higs missile launchers.   That way none of the others can shoot or melee you from behind, which happened to me a few times.   Nothing sucks worse than getting this far and having to start all over again.   Replace your missile launcher with another gun and finish off the last few Higs still advancing on you.  Once you've taken these guys out, all threats have been eliminated.  Advance into the engine room. 

Hope this is helpful. 

Cheers.

Elite Difficulty is brutal! i really dont think that i can earn that trophy.
That last area of the game is tough theres extremly little effective cover!
Its difficult on normal...
And i was really hoping for that platnium.
Has any one here done it?

Btw good luck buddy!

I hate this game's story.  I never planed on playing it for story so it isn't a down point for me.  But damn, does the single player suck a lot of balls (not saying that being gay is bad).

It wasnt infinite respawn for me. I got the enemies to follow me back out to the previous platform and i levelled them with the turret on the tank. I did this a few times and then went back and seemed to have plenty of time to pick up an rpg and blast the tank.