The opponent is at the door and is planning an attack. We all know it, you want to destroy him immediately for this insolence.
HOWEVER! Don't be tempted.
The SAMs are an important tactical defence weapon. If the opponent wants to attack, let him come! Never be tempted, always stay in the protection of your SAM, so the enemy has to take the fire of your SAM and your units if he wants to destroy your units. If you drive to the enemy, you will unnecessarily lose more units than you need to.
If the opponent comes, drive behind the base
Even better is: if the opponent comes, drive away behind the base at the sides, so that the opponent has to drive after you and can be shot even more by the SAM on the longer way and the opponent has a longer way back on top of that, should he have something left.