I've used dry transfers for lots of things. They're pretty easy to work with, and you can reproduce pretty small graphics with them. However, they're at their best on a smooth surface. Any kind of surface detail gets in the way of a clean "rub down" and can distort the image.
The billboard lettering and the road number are dry transfers. The rest are from Microscale decal sets.
I used the same set of billboard lettering on this, which was a pain to align with the ribs, but a little time and a little patience brought out results that were good enough to obliterate with weathering and a restencil...
You can rub the lettering onto decal film, then seal them with decal finisher. It gets to be a little thick though.
I had them made at Advance Litho in Baltimore. I'm not sure if they're even around anymore.
They've held up extremely well. I had them made in 1991 or thereabouts, and I still have occasion to use them. I keep them in a ziploc bag to keep the cat hair to a minimum, and to keep them from drying out.
Lee