Thanks for some of the suggestions. One of my wife's colleagues is a science teacher and he suggested to soak the rubber down with a silicone and place them is a seal-able container for a minimum of 10 days. The 1/8 tire seem to spring back after a few days and looks pretty good, is a little softer than it was. The 1/12 Tamiya looks a little better and is pretty soft. At this stage if I add some foam as suggested to the inside of it, it should look pretty good. I think I will soak it for a few more days and post the results.