I would say that damage goes far beyond gel coat stress cracks. This brings up the issue of trailering and engine supports which always proves to be a controversial subject at best. After many years, I much prefer the supports that drop to the trailer frame. While I agree that trailer vibrations bumps get transfered somewhat to the engine components, I've never experienced any issue from that. If you think about it, the engine stops that don't transfer some load to the trailer directlly, are constantly stressing the transom area all the time with no relief there. Some say that that's not a problem- transoms are made to handle that. I believe that the stress placed on the transom during towing is entirely different than the stress on the transom in the water with the engine in operation. At some point I would rather fix a wear issue with the engine than try to have a transom repaired.. Since I've never had an engine issue with a trailer bar support, I'm not switching to the newer models.
All that said, I can understand your pain and frustration. That will be a costly repair if done properly...