The AT-2 is the obvious choice for this achievement. Don't even think about attempting the achievement unless you are top tier.
Try to push with the main force, whichever way it goes, and get to the front of the line. The difficult part of using the AT-2 is that you will need to be hit A LOT by these low tier guns. But you should get paired up with a bunch of seals, and then its just a matter of watching the damage deflected icon until you reach 1000.
The other important tip is that its important to face several tanks and hope all of their shots deflect. Even the dumbest players will stop shooting eventually when they discover that they aren't doing any damage. So 1 guy isn't likely to shoot you 20 times. Thus why it's important to stick to the front and face off against the enemy team's main push. I got it with 6 different tanks shooting at me in a matter of seconds.
Once you have 1000 deflected, back up carefully and hide, hoping that your team can pull it off.
Stick with it, you will get it with the AT-2. Everyone in my platoon who has run this British TD line has gotten the achievement, including guys who aren't even achievement junkies like us. It will come.