I can think of hundreds of things to do to make my trailer my own and decorated my way without the expense of changing the cushion covers.
Here's a couple simple ideas hopefully to start the creative juices flowing. First small pieces of clear plastic, available at home improvement stores, and pictures. Cut the plastic smaller than the door and hold in place with mirror hangers with pictures behind the plastic.
As was mentioned earlier, make pillows that are covered with your choice of pattern.
Replace the curtains with your choice of pattern.
I wouldn't change the interior color and paint
on the interior fiberglass, but I might paint
on the cabinet doors. The brown strips around the top edge of the counter top is easily changed to another color. I'm about to turn mine red.
Hot pads with nice patterns can add a nice touch. I used lamp hooks attached to a small piece of wood then held in place with self adhesive Velcro to hand the pot holders.
OK, I hope that will start the creative juices flowing.