The factory one piece tube was developed in conjunction with Carbon Arms I'm lead to believe although it's not as good.
I've been toying with a Roth one for a while but not living in the US was struggling to get one shipped to me. So I'm pretty gutted they've stopped making them as well.
I did get all the bits to make a one piece tube in a similar design to the carbon arms one I've just not got around to doing it.
I did think about the factory tactical one piece as well. But even when Remington still existed and you could buy spares they never listed all the parts required to do it.