Trips to the outside require a great deal of coordination. Resting up before the trek. The crash and necessary additional rest afterwards. It's easier to just stay home. All the benefits without the worry about her ever writing any of those pesky memoirs later.
Ghost writers sign nondisclosure agreements, after all.
Beyond that, there are few requirements or restrictions. In this theoretical relationship, the guy sets her up in, say, a condo on a lake. The second phone line for the Internet access is a given. A well-read mistress is a contented one, I've heard. A PWC could take the easy way out and go in search of a nice wealthy widower, but then he might want a social life.