I think as the OP has the solid colour cushions rather than the plaids used in the past it would be pretty easy to dress the trailer up without changing the covers. Actually a lot of designers would suggest that having a solid colour is better as you can easily change the whole look of the trailer by simple replacing the accents - much cheaper as well. As other have said changing out the curtains and pillows and putting down a throw rug will change things up a lot. As will adding kitchen/cooking accessories, towels, kettle, large utensils in bright colours. If your going to leave your bed made up then a bright bed cover will also make a really big change as it will leave very few of the orignal cushions visible anyways.
I originally thought I was going to use a pattern on my cushions when I redid them but got talked out of it by a pro decorator at the home decorating store i purchased my fabric from. I ended up going with a solid colour on the cushions and a pattern on the curtains instead. That provided me with a lot of options as to what accent colour to use on my accessories. Kind of glad I did as after the first couple of years I did decide to change the accent colour to freshen up the look of the trailer. You can also change out the curtains pretty cheaply and fast as well - recommend you line them with a light thermal curtain backing with a bit of stain resistant film on the back
though. The lining makes them hang much nicer and prevents moisture from the windows
soaking into them and prevents sun damage to the bright colours that are on them.
Hard to tell from the photo but it looks like there are a lot of bold colours that would work with the colour of the current cushions - reds, lime green, teal blue and yellow to name just a few. I would take one of the covers to a large fabric shop and see what you can find that works with it.