Personally I would not wash it in fear of any colors that are present fading, especially on the painted stripes. Besides being dusted off, I think it looks just great how it is and probably didn't look too far from that condition the last time your uncle used it. I would just dust it off the best I could and remove the little nests of course haha, But other than that, I would just be too weary. Remember, some of that dirt and stains has to be from the time he spent serving and after he landed on the beach. Just my two cents