That's what I do on long distance train trips - book a Roomette for only part of the train ride.
I don't upgrade once i'm on the train. I just book the trip that way when I make the reservation.
Beaumont or Houston to Alpine would get you, dinner and a shower, and breakfast and anothere shower the next morning.
Going from Ottumwa, Iowa to Emeyrville, CA - I book coach from Ottumwa to Denver, a Roomette from Denver to Reno, and back to coach from Reno to Emeryville.
Denver to Reno is about 25 hours and overnight. I get 4 meals (breakfast, lunch, dinner, breakfast) with the roomette and I shower twice.
On the way back I have the Roomette from Reno to Denver - dinner, breakfast, lunch, dinner.
On an upcoming trip on the Texas Eagle from Chicago to LA I'll have a sleeper from Marshall, TX to Alpine, TX - about 27.5 hours.