Old trunks and odors go together like honey and bees.  You're glad you found the former until you notice the latter.  Most odors can be dealt with if you can bear to be patient.  It took 100 years to build up that smell - you can't get rid of it in an afternoon.

First and foremost, nothing helps get rid of odors better than fresh air and sunshine.  Why do you think those retirement homes roll all the residents out on the porch whenever the sun comes out?  If your trunk smells musty, leave it open out in the sun as much as possible.

Check out the inside of your trunk.  What is it lined with?  Most are lined with paper, and it usually isn't in mint condition.  Get rid of it!  It stinks!  Scrape it out and sand down the wood beneath.  If the paper is too hard to scrape, try dampening it with a sponge.  I said dampen it - don't soak it with the garden hose.  You can stain and finish the wood for a nice look.  For goodness sake do the right thing and use a low-VOC or water-based finish.  If you dampened the liner paper to remove it be sure the wood dries thoroughly before you apply stain or finish.  This little exercise will leave your trunk looking and smelling better.  It even works pretty well for that mothball odor that makes your eyes water.

Here's a tip sent in by Jo Ann Cross:  Place an open bag of kitty litter in trunk and close.  Check it in about a week.  The cheap brands
usually work the best.  Thanks for the tip, Jo Ann.

A wise old trunkster once told me to put a lit candle inside your trunk and then prop the lid open only an inch or so, to let air flow so the candle will burn.  He claimed it would work wonders on almost any smell, and that it was the best way to treat mothball odors.  I learned a lot from him, that old gent, and I really miss him since he passed away in that big fire.  You probably saw that coming.