We have a 3326 King and the microwave is built in where the oven goes. We have a 13 inch GE color tv that I place on the floor in front of the couch. The floor in front of the couch is part of the slide out and is wide enough for it to fit nicely. Our big chair goes in the entrance way when the slide out is pushed in. We have never had any problem with it moving. I always make certain that the picture tube is facing the couch.
In our 1994 3326 King, we had the oven and bought a small portable microwave. I always put it on the floor next to the wardrobe which was lying on the floor. I had small pieces of foam that I put on the sides and also next to the wardrobe to prevent scratching. Never had any problems. With the 2002 model, the microwave is built in and sure makes it a lot handier.
Your 3124KS model will have the same front slide out as our trailer. So doing what I do should work fine.
If you have any other questions, just let me know.
Bob Strong