What is a good Terran anti aircraft strategy if you are on the move?

Solution 1:

Vikings make great AA if you are on the move. They tend to outrange most Protoss aircraft (besides their sieging air). They are also extremely mobile and so you can do a lot of hit and run isolating units that get stranded out.

I wouldn't rely on Vikings as your only AA though. If the enemy is pretty much an aerial based enemy, mixing in Thors do really well since they are extremely healthy units and also do aoe damage to air (light armor in particular). Mixing in marines with your spare minerals is pretty key too. Use Marines and Vikings to focus individual isolated units in fights and have your Thors focus on the largest clumps of enemies. If you are very good at microing, it is worth mixing a few Ghosts into your army. You can use their EMP to eliminate enemy shield which greatly helps.

If the enemy has Colossus, try to have your Vikings and Banshees focus those first. They just completely shred Marines and Marines are an extremely high source of damage so you really want to protect them if you can.

EDIT: The other answer also suggested bringing SCVs in order to repair Vikings. It's a good idea to bring SCVs to repair your Thors also as well as Vikings/Banshees.

Solution 2:

Your best bet in this case would be Vikings. You already have the Starport, so build a Viking for each Banshee.

If you have SCV's in your army, the SCV's can also repair the Vikings.

It's important to rule the sky against Protoss so they don't overwhelm your army with Void Rays and Tempests.

You can also use the Vikings to deal with the Colossus so your Marines won't die as fast.