The pictures here show an assault using Lancer Bunkers but this method works equally well with Machine Gun Bunkers at earlier stages in the game and works well with Scourge Missile Towers at later points in the game.
When you have discovered the enemy base then assemble 4 trucks ready for an attack.
Now use 3 of your trucks to construct a line of Bunkers right up to the front line.
With the 4th truck build a Sensor Tower to improve the range of your Lancers. This is not necessary for a Machine Gun Bunker assault as they do not benefit from any extra range.
The beauty of the straight line attack is that each bunker is in the front line for a short time before it is relieved by a new one built in front of it.
You might lose some trucks dong this but that should not be a large concern.
In the picture below I have lost 3 of my four trucks and have sent my 4th truck in to repair the front line bucker.
Below, it is clear that nearly all structures within range have been destroyed and it is time for a second thrust into the base. I have reinforced the number of trucks to speed up the attack a little. You can see from the research above that I am continually improving my 'crete to make it harder for the enemy to defeat me. You can also research damage and fire rate improving techologies.
In the picture below you should note that I have built another Sensor Tower, built a Derek and nearly completed the next line. I also lost all my trucks. An artifact appeared in the path of my bunkers and you cannot build over them. The entrance to the enemy base is is to the right and he will not be able to have one vehicle leave it without facing a barrage of Lancers.
More of the same. New Trucks, a line of Lancers right into the heart of the base.
With the row completed it is only a few minutes before the base is yours. One huge advantage here is that after you have claimed the new base, another enemy will find it impossible to get past all those Lancers. Your attack structures become your defense.
A few notes of interest with this particular method. The cost in structures to do this attack was about 4200 oil plus the replacement trucks of about 1200. This cost is spread out over a long time period and you can stop and come back to the attack at later time with virtually no penalty. A vehicle based attack cannot be resumed in the same way. A smart player will build oil Dereks as soon as possible to recoup the oil cost more quickly.