If the R.s knew the important things about the down-spiralling marriage of SM/BM (and I think, they did), the two would have been the right reliable people to hide Suzanne's diary for her. What a pity, that Suzanne kept it in the home, where her future killer sniffed around.
If MR was involved in searching for Suzanne with BM on his side, I can imagine, he noticed some oddities with BM and had his own thoughts to things going on and was able to form a bigger picture of past and present occurences. The previous owners of the PP home even had negative thoughts of BM already and only during selling their home to BM (so a relative short time span); then the R.s would have known much more, IMO.
Whether BM stayed at the R.s, I don't know. I remember, he was staying with
a buddy of him (ff?), who talked about the way, BM paced up and down and was looking out the window all the time. At the time, when I read it, I didn't think of BM staying at a property, where he was able to watch going-ons on his own property. I thought, it was an expression of his nervous restlessness only. - Maybe, I didn't understand it the right way.
ETA:
The fire chief has not had direct contact with Barry Morphew since Suzanne disappeared, but has spoken to firefighters who have. He said that Barry is staying with a friend in the area, “pacing around, staring out windows,” hoping for information about his wife. The friend is not a member of the fire department, Bertram said, though some Chaffee County firefighters have seen Barry at the friend’s home since the investigation began.
‘Pacing around, staring out windows’: Chaffee County Fire Chief addresses questions about missing Suzanne Morphew’s husband Barry Morphew
& Dateline) w clue related to a storage unit rented by the perp.