A vintage trailer is like a vintage small house: It forces you to be creative about storage and to maximize space where and how you can.
I found small, coated-wire baskets (Dollar Tree, $1 each) that fit neatly inside the over-sink cupboard of my trailer. Using napkins for padding, I set heavier items, like metal bowls and silverware, inside those containers. This keeps them from rolling around during transit and popping the cupboard doors open.
Then I used a metal shelf-riser (from the kitchen/bath storage section at Ross) to create a second tier of shelf space. It holds lightweight items, such as silk flowers or paper goods--things that won't force the door open if I happen to hit a bump or pothole.
I've found that I get more use and better storage from my small trailer sink if I keep an enamel bowl in the sink. It's easier to pitch a small bowl of wash water than to drain and clean the sink. The bowl keeps necessities handy (glasses, watch, phone) and I still can tuck other items, like towels, around the outside of the bowl.
By adding another shelf-riser over the sink, I gain extra flat surface area--something you never have too much of in a small trailer.
This is another of my favorite ways to get extra surface space--by placing an old metal serving tray over the sink. Also a great way to hide the clutter-bits when someone comes over to visit your trailer!
Here's another way to utilize a shelf-riser and serving tray. And once you have these simple extras in hand, I'm sure you'll find other ways to put them to work in your vintage trailer!