Almost all steel rims rust on the inside. Water gets in around the spokes. If the chrome is really good on the outside and you want to keep them chromed, then wire brush the inside to get rid of the scale and smooth things out. Then spray the inside with a good rust converter which stops further rusting. Just paint the inside and put on a new rim strap. As long as you stop the rust and remove any roughness that will abrade or puncture the tube you are good to go. To keep moisture out, some will seal each spoke on the inside with a dab of silicone before putting the rim strap on. No one will ever see the inside of your rims but you.