Sorry to hear of your loss. I have been flying for 15 years and can tell you from experience, that in this hobby, you will lose a few planes. Some will be due to your fault, many due to mechanical or electronic failure. However, with that in mind, there are ways to reduce your chances of failure. I was not there in your situation and it hard to conclude IF there may have been another factor that may have added to the problem.
Based on the info you have provided so far, a one time soaking of fuel on the fuselage WILL NOT inherrently reduce the structural intergrity of the balsa provided that you did a thorough job of removing the fuel. Also, based on info you provided, I would also note that having a experienced pilot fly the plane after the repair woudl have been adviseable.
I also have the 4 star in ARF and Kit form and have had no problem with either. I would agree with fellow moderlers who have suggested to you that you send them a pic with testimony to SIG of your situation and see if they may replace your airplane. Depending on your demeanor in the approach, I think you will find a satisfied reply. I wish you the best of luck on this issue and hope that you do not give up on ARF's or flying.
Hang in there, and just be prepared to buy another plane, radio, and engine if need be. I've done it! it's part of the risk!