I've done 5 RSE trips solo and 6 trips w/people I met on RSE--we enjoyed each other's company and were able to travel together on other tours. One of my roommates and I were so compatible we traveled together independently and w/RSE until cancer ended her life. My reason for choosing RSE trips initially was that there was no single supplement making travel affordable. I once split a single supplement with 2 other travelers and we rotated the single room throughout the trip. Don't try and travel as a triple w/o splitting a single supplement-as I learned from experience (3 adults in a "doll house" requiring you to call out when you were getting up from the bed (dosey-doe your partner) - 2 twins and a cot designed for a short child, luggage needed to be stored, and slept with, on your tiny bed because there was no place to put it - and the bathroom/shower situation was miserable trying to get ready on time).
The courtesy suggestions written by the first person responding to your post are critical when rooming with a stranger. My first trip I had a roommate for the entire trip. I announced at the first group meeting that I would love to share meals with others and even made reservations for our free time. This worked very well. My roommate and I got along, although she was terribly disappointed when she went on her day off with other travelers and never saw the item high on her list because they prioritized their sights higher. Don't be afraid to go off on your own to see what you want to see independently. I have experienced a number of couples with the mindset that singles are a nuisance and you should be prepared to change your seat at a table, in a gathering, at a site, etc., so that the couple can be together. I don't play that game. I pleasantly but firmly stand my ground.
On my second trip, there were 5 singles and we rotated rooms; however, when it was clear that one of the singles was opposed to bathing and smoked in the room, we 4 agreed to give her the single room for the remainder of the trip but had to involve the guide after the guide tried to force one of us to continue to room with her. It was on this trip I met my travel buddy and we traveled together for several years.
My next solo trip I roomed with a very pleasant person; while we did not travel together after or become best friends, we got along just fine.
The next solo trip I had the roommate from H-E-double L. Heavy perfume user. Would not compromise. Ordered me where to put luggage, which bed I could sleep in, what I should wear while criticizing my wardrobe, monopolized (locked herself in) the bathroom every morning from 4:30 am until 7:30 am and only grudgingly let me in to use the toilet after begging, constantly complained about other tour members, the guide, the tour, the activity levels, being responsible for her own luggage, refused to let me open a window or turn on a fan or A/C, and so much more. I'm used to trying to make sure everything is comfortable and pleasant for my roommate and I didn't want to be known as "the grump", so I let it fester, didn't spend time in the room, but finally blew up at her at the end. My bad. When you have a crappy roommate, involve the guide early on. Fortunately I met a wonderful traveler on this trip and we've taken other tours together plus she introduced me to another like minded traveler.
My last solo RSE trip was several years ago and for the first time, I was the only solo traveler. I missed the camaraderie that a roommate can provide. It was a shorter trip and I didn't get a chance to gel with some of the couples until closer to the end. I'd be a bit more extroverted at the beginning if I had to do it over. I'm contemplating another solo trip soon and am considering "chancing" it and not paying the single supplement since it really eats into my budget. I've paid single supplement on other non-RSE tours where there was no choice-hard on the budget. Happy travels!