Sorry to hear this sad news. A young man loosing his parents. I do believe in the God of mercy and love, and will pray for Ethan. (I won't easily forget his name, because my brother has a grandson by the same name, and roughly the same age, just a bit older, i think.)
I was a stranger to this practice of putting up a memorial at the accident site until my daughter's boyfriend was killed in an auto accident not far from our home. We put up a cross we had made, and it stayed up for some years, but later a road crew did some work on that stretch and it disappeared. So keeping it in the fence row is a good idea. (We had it close to the fence, but it was just an electric fence, so not so permanent.) I've wondered what the custom is for how long these should be kept up, before you bring it home to keep it. (We are still good friends with his parents, who treat our daughter like a daughter to them as well, and her children like they were their own grandchildren.)
I hope that his work on this cross will be meaningful for him, and will in some way help him get through this. But most of all, for the grace of God to hold him up. (I hope I'm not getting too "religious" here, but in the book of James it says that true religion is looking after the needs of widows and orphans.)
Nice Neto