Let`s do some basic math lol. 5% of 1000 is 50..5% of 2000 is 100.. 5% of 3000 is 150.
the only tank ingame with 3000HP is the German Tier X Heavy, the Maus..
most Light tanks and Arty have less than 1500HP..and most do not even break the 500-1000HP mark,
Mediums have an average HP pool in thier tier match ups.,
Heavys and Tank Destroyers have the most HP and the highest survivability of all the classes.
The smartest way to do this cheevo is to play a tank which you are good at, no matter the tier or class and simply try and take out as many enemies, while taking damage. If you manage to get enough kills and have only less than 5% of your HP left, there is a good chance your team will win the match. once you have less than 5% of your life, you can do 2 things. either run and hide in hopes your team does the work for the win or you can help and snipe, playing defensively once you are low on HP.
The cheesy way of doing this cheevo would be simply yoloing any tank, rush the enemy at spawn, get hit (without dying) and leaving -5% HP left then go run and hide in hopes your team wins the match for you.
Just remember, if you sit at your spawn point or base camp, if and when the enemy team comes close to your base, most likely your team is already losing the match and you will not get the cheevo for losing even if you do have -5% HP.
If you want to increase your chance of winning the match, while getting damage, I would suggest picking any tank in your garage with a ridiculous amount of HP, ie a Heavy or Tank Destroyer. Play normally, assault the enemy, kill a few off, while taking damage.
If your team is winning the match, and you are still at full health or still above the 5% HP mark, expose yourself and get hit.. just don`t expose your rear or your obvious weakspots. ie sides or gas tanks or ammo rack. The best way to get hurt slowly is to have a tank with strong frontal armour or well sloped hulls and turrets and play peek a boo from corners or a hull down position, Expose yourself and let the enemy shoot you... and because you have a good tank for playing defensively, you will get only min dmg done to your tank while hull down. Also, if you find yourself being shot at and the enemy is not damaging you because your tanks armour is amazing, you may want to show your rear or sides to the firing enemy so they can damage you, and once you have -5% HP, face them with your strong armour or run and hide
HT and TDs are great for the tactic above playing defensively to kill and get dmg yourself. These two classes are good at surviving even when you have -5% HP left.
some examples of tanks which take a beating due to strong armour. Please note these are my suggestions but there are countless other tanks which can do the job to pop the cheevo, it`s the players preference and skill using that particular tank.
UK AT series, USA T28 and the T28 Prot, E4 and E3 tier Xs, T29 and the E5
German Maus, VK 42B, E100, JPE100, Tier IV DW2 and most of the mid tier VKs have high survivability.
Russian IS lines have high survivability due to the round turrets and sloped armour.
Mediums are great for hit and run tactics, dwindling down the enemy team while getting damage yourself and being able to to run and hide when your HP is -5%.