Since I planned to use epoxy and spar varnish to protect the outside of the trailer I had to use something compatible with that underneath to color the wood. Oil based stains prevent the epoxy from adhering so I had been given some helpful advice to try aniline dye. In my tests the aniline dye worked great. Since it is water based and stays near the surface of the wood it is easy to blend even after it has dried. This helps since I had a large surface area to cover.
I have only been able to find 2 sources for the powder dye. Transfast from Woodcraft, and J.E. Mosers from Woodworkers Supply. I ended up choosing J.E. Mosers Dark Colonial Red Mahogany color. Be careful, as I had wide color differences between batches. It ended up taking less than 1 quart (1oz powder) to do the whole trailer.
To get the aniline dye applied correctly it is necessary to raise the grain on the wood. This involves wiping the wood down with a wet rag to raise the grain, followed by a light sanding to knock it back down.
Using a damp cloth pad I started applying the dye on the trailer.
The last application drying. If you find any areas that are too light or dark you can go back and even out those areas even after it has dried.
When I pulled up the painters tape I had some bleed from the dye. Luckily a light sanding cleaned it up as the dye stays near the surface.
Here is the final result after the dye was applied.