I am hoping to make it as original as I can for my budget and it was pained when new, oh and the wood I got cheaply has a name stencilled on the side so I have to cover that
I wouldn't paint a trailer if I could - it is too easy to scratch the paint during use, water gets in & lifts the paint & rots the wood. Creosote & waste oil is best but messy, a good oil based fence paint like Cuprinol garden wood preserver would be my choice and should cover up the writing on the wood.
If you're set on painting it use a good preserver, try to soak the boards in it. Finish with 2 coats of a decent oil based primer like crown or dulux and 2 coats of gloss.
Once I finish working on the wood prior to adding a finish (varnish, paint, stain) I wipe down with mineral turps and then let it dry for ten minutes. It gets all that sawdust you can't see and the stuff that doesn't brush out. A real old school guy taught me that, he also uses kerosene to flush out woodworm. Highly effective but makes your timber flammable!