Registration of a visa for Russia during a stay on the move

In Russia, the host must register a stranger a week after his arrival (assuming it remains more than a week). How do independent travelers not staying in hotels all do? For example, I could spend the first three nights in the train and the rest in trekking in a national park. People can also drive a motorhome and use it to sleep. I read that If you take the Trans-Siberian route by train and sleep on it, then the train ticket will be equivalent to the check-in (you should always keep your ticket at hand). – Does this mean that the Russian railways are registering abroad? Can they also do it if I spend two nights on the train to a national destination without going into ordinary accommodation from there? How does this work?