An off base assault is an assault in which you build bases close to the enemy's base. A good map for this is Corona Chasm. It has 4 main starting points, and some small islands. To execute an off base assault, build a base with as little as a few point defenses on the islands. This gives you a shorter distance for attacks, and a better view of the enemy.
You can use these bases in multiple ways. If you are on the same land mass as your enemy, you will want to be careful of enemy units simply rushing into your puny defence and crushing it. Consider first constructing point defenses and shields, and if you are planning to make a real stand, build nuke defenses. Once the shields and point defenses are up build some factories, and be sure to protect the factories with shields so missiles can't prey on them.
You now have a fully good base, but don't stop there, these bases can become huge, even competing against a main base. If you have the resources build nuke silos. They will be safe if your enemy nukes your main base, so you can release them all at once. Stock them so you can devastate the enemy. Strategy