I would agree with wipe on poly as well. I've used it to good effect on my frankenbass body (after grain filler and stain) and on a few necks. This body got 9 coats of what I think was just hardware store bought "Formby's" satin wipe-on poly.
My new T-40/Wal/Decade'ish Frankenbass
It's super easy to use (as easy as tung oil) and you can layer it as much as you want. It's not as strong as a 2-part catalyzing finish or a really thick layer of sprayed auto-body style poly, but it's FAR sturdier than oil. I've done an oil finish on a body once and it was a dent magnet. It's fine for some necks, but I'll never do a tung oil body again.
If you like the "raw wood" feel, you can probably just wipe the poly on right over the existing finish. Otherwise I'd sand it back a bit and then fill the grain and then poly.