Keeping it painted means easy. You just fill them with latex caulk a couple of times before you repaint. 1st application is to force caulk into the crack and 2nd application is to smooth the caulk to the existing paint for a seamless look from any angle.
- Staining may be a lot of trial and error, so get some scrap(s) from him and put gouges in it or them. There are plenty of Wood Putties or Wood Fillers and they are stainable. But, they don't and can't take stain the same as wood, due to their adhesive ingredients. Then, stain away until 1 works for you and your stain color, ask store staff for assistance.