This mission is indeed an absolute nightmare!
First of all, you have to survive the initial battle with the Imperial patrol right at the beginning.
After that, it's a matter of using your 2 scanner jammers to reveal areas of the map around you, then using your vehicles with long range weapons (i.e. proton-missle launchers) to knock out any vehicles that you might happen to see. DO NOT MOVE THE BULK OF YOUR FORCES INTO AN AREA THAT YOU HAVE NOT CLEARED.
In some areas of the map, barges will come down to replace the units you have killed. It's best to avoid these. I went west from the initial starting position (until you reach the water) then north a little, then northeast to the centre of the map. From here you can knock out the fixed artillery turrets lining the south edge of the river. You also avoid the imperial units that will get replaced once they are destroyed.
This strategy does work, but it is very trial-and-error and VERY time consuming. It gets very frustrating waiting for the scanner jammers to charge back up again.
You might also be lucky enough to nab an AT-AT with your infiltrators.