

Sleeping as part of a car journey in the car is allowed. Wild camping is generally forbidden although Bivak/Sleeping bag in a Schutzhütte perhaps even in a bus stop is allowed as part of travel.
All that said if nobody notices you, there’s gonna be no trouble, and even if somebody notices your camp the worst they’ll likely do is tell you to pack and leave.
Otherwise try sleeping one driver on the ferry i guess.
If you have rail standards of the 21st century cellular is absolutely what you should be using for rail see: GSM-R . Apparently the DOT is even looking at this.
Now you’d need to build cellular infrastructure along your lines for that system. US rail owners are terminally uninterested in building or maintaining rail infrastructure so that’s not particularly likely to happen unless mandated.