Xtrusion overland has a rack that they are making for the M416. they are hugely customizable. I'm not affiliated in any way with them, but I have one on my Gladiator. You might check them out. Warning, I understand it takes a long time to get their products. They are a pretty small company.
bump...
I'm travelling from middle TN (Nashville) to FL (Orlando) at the End of September. I could deliver it on my way if anyone is interested. You would have to meet me on my route and there would have to be some upfront payment or non-refundable deposit. Trailer is not perfect, could use...