Here're some tips. Took me an hour to get the attack pattern down, and even then I don't remember it all... but still:
Wait for the first strider to come near to the sawmill before blowing it up since you'll need to save the time for the second one that comes around at high speed. Drive the car up to the water tower and blow up the third one with the bomb on the car, then keep driving towards the supplies shed (from sawmill to water tower, just follow the road) and restock your M device. Drive back towards the sawmill and do your damndest best to blow up the running strider coming from the Cranes (he goes straight rather than turn towards the sawmill). There's a small reprieve, so restock. I recommend a quicksave around this time.
The next one, IIRC, should be the water tower or Sawmill. My memory is fuzzy, and there are a few more, but once the major wave is defeated you have a little time to restock again, the first of the last wave of striders comes from the Cranes, then Sawmill, Tower, Sawmill if I'm not wrong.
Here's my winning secret: You can grab the M devices with the gravity gun, and drop them without blowing them up with the secondary fire. This way you can create a huge stock of pre-loaded bombs at the two major sites which you need to protect during the earning of the achievement. These work pretty well against Hunters too. One bomb and a physics object will kill them on Normal.