I just wanted to write something about this, because I find it ever such a nice touch by Trollope. It's something I haven't come across (so far) in classic literature. Most authors seem to limit themselves to the 'proper' places, even for married couples, and forego the only really private room they have. Most of them therefore don't go further than private moments on strolls or in drawing rooms.
The well-known couple-together-in-bed scene in comedies (think of Onslow and Daisy in Keeping up Appearances) and drama (various couples in Downton Abbey) is a peak into a couple's really private sphere. The bedroom is a rare private place, particularly in the world of 19th-century high society, where no-one, not even a couple's family, can see or hear them, so characters drop the masks they (are compelled to) wear day in day out and they can say really what they think (of each other and of the rest of the world).
It started in The Warden with the Archdeacon ranting about Hiram's hospital to his wife, but the Honorable George de Courcy and his kind of slightly clueless though wealthy wife were another lovely touch.
Shows you these scenes have a long tradition indeed... And Laurel and Hardy were not at all the first to sit in bed together for comic effect.