It seems that every time I log in, I get raiders...they chew through my defenses...and I constantly get fires or more raiders a lot of the time right before i'm about to hit the main menu button...arrrrggg lol.

Get your two best guns and two best armors, put them on your two hardiest vault dwellers, and then have them stand sentry in the door room. Zoom in and stand by with the stimpaks to keep your guards in fighting form. Drag 'n drop your door guards into whatever rooms the raiders go to; any other dwellers in the rooms that get displaced by the door guards entering will simply return when the crisis is averted (as will the guards to the door room). Be sure to upgrade that vault door too so it's hardier against the raiders and you have more time to get other gunners in the most likely rooms beyond the door room that the raiders will go to. For me now, two raiders never make it past the door room, and the third never makes it past the top floor.

The main threat you will face later are the Murder Roaches. Gah.

EDIT: Some thoughts on the Murder Roaches: They can come into any room, not just through the gear door. With raiders, you also have time to prep a defense with hardened dwellers as they attempt to breach the door. Murder roaches can pop up right in the middle of a room potentially full of squishy workers with no warning. I noticed that if I brought my door guards to bear on the murder roaches, the infestation was eradicated pretty quickly.

Been hit by raiders 3 times today. Just get things built up from the previous attack and another one hits.