The reference you may be thinking of is mentioned in a letter to John
McComb 6(?) Feb. 1870.  The original letter is apparently lost.  The
transcription from newspaper publication is online at:
https://www.marktwainproject.org/xtf/view?docId=letters/UCCL00420.xml;query=Palace%20car;searchAll=yes;sectionType1=text;sectionType2=explanatorynotes;sectionType3=editorialmatter;sectionType4=textualapparatus;sectionType5=;style=letter;brand=mtp#1

Barb

On Saturday, August 21, 2021, Scott Holmes <[log in to unmask]> wrote:

> I've gotten hints that Mark Twain had available to him, at least briefly,
> a luxury railroad car, probably made available to him by his
> father-in-law.  I would appreciate any leads on this as Google seems to
> know nothing about it.  I did see the term "hotel" used to describe a car
> Twain rode in, possibly  from Elmira to New York, if I'm not mistaken.
>