This model had wood grain molded into the upper back interior panels. I just painted it to look like wood. The rest of the interior, I actually "grained". I've been using Testors acryl lately to do that, and usually start with a base coat of tan, depending on what kind of wood I'm trying to replicate. Then build up layers of other colors like brown, orange, yellow, leather, wood, and black to give the wood more variation and depth. I dry brush these (wipe any of the excess paint on paper) before applying to give the grain effect. Sometimes I use a wide, flat bristle brush, especially on larger areas to give the graining look. A liner brush and black or dark brown can give the grain lines. A fine point Sharpie can also work. The paint must be dry between each level or it gums up. You can apply different matte or gloss finishes as a top coat, depending on what look you're aiming for. It isn't as difficult as it sounds, just give it a try on some scrap first.
Here are some examples. This one is a '29 Ford Custom Woody I did, and I painted the wood grain on the body and the surfboard here.
Here's a '58 Ford Thunderbird "Tiki Bird", with wood grain across the front, sides, back and interior pieces.
And lastly, here's a piece I'm doing for an early '20s Olds truck.
Hopefully you can see some of the different types of graining here. You can see how each of them has different colors blended together to give it more of an authentic look, as opposed to just using one or two colors.
Anyways, thanks for the comments and I hope this helps a bit!