Tony is right about the shellac. It's the most versatile finish out there, in fact many of the "hi-tech" primers are actually shellac based. But there are a couple of important points you've got to be mindful of. Some finishes, primarily polyurethane, are not compatible with waxed shellac. You've got to use dewaxed if you're going to put poly over it, or the poly won't stick properly. If you use premixed, canned shellac, the regular cans are all waxed, including the spray cans. The shellac sanding sealers, like Seal Coat are the only cans that are dewaxed. Seal Coat is a good shellac that is just a little thinner than the regular cans. The spray is even thinner. You can learn everything you need to know about shellac here:
Personally, it makes me sad to see woodwork painted. My research suggested that the wood in older Airstreams was finished with toned lacquer, ie; lacquer with dye mixed in. It's best to apply a sealer (like shellac) then apply light coats of toned lacquer to the wood to get the right color. Then apply a clear coat of lacquer. This is the process I'm working on right now. It's easier than it sounds.
Most people sand, stain, and apply polyurethane. It's a good approach, but getting stain to get to the right color is challenging, especially of you want a lighter color. My biggest complaint about this process is that poly dries slowly, so keeping dust out of the finish is difficult.