Check out M4 Products
. They have a bulb base identifier at the top of the page and you can see most bases on the home page. They're probably 1156 base for bulbs and G4/T4 pin for any halogen lights. Their prices are a little higher than the cheapest you'll find on places like amazon etc, but they use top notch LED's that produce more light, which you'll be glad for later. They also provide diffenent light quality so you can choose from cool white natural white and warm white to suit your desires. Natural white is more like daylight, good amount of natural feeling bright light. Warm white feels a little more like the incandescent bulb, a warm yellowish glow, cozy cabin feel, Cool white, lots of bright light, it's a little bluer so may not feel right to some.
Friendly return policy so you can order some different ones to get a feel for the colors and light quantity, and then return the ones you don't like and order all you need for the trailer.