advice on rehabilitating a stray turned slightly feral

I have a TNR trap and have caught a male whom I assumed was feral but, after spending 3 days with him, I now believe he is a stray who has spent a long time on the streets abandoned or lost. He allowed me to pet him, move around him freely, and lift him from one cage to another, although he eyes me with suspicion. I have decided to try to foster him for rehabilitation and eventual adoption rather than releasing him to the wild again. Unfortunately, my own cat does not respond well to other cats in the house and keeping him would be traumatizing to them both. But until I find a foster, I need advice on what to do and not to do to rehabilitate him.I let him out of the trap, in the bathroom, and he is currently hunkered under the vanity and does not appreciate any advance on his position. This, of course, is not an ideal location for him. Any advice is appreciated or suggestions on how to find a foster family (all the local facilities (Tucson) are full and rather unhelpful). I had him neutered and vaccinated. I have rescued 7 other ferals this summer so I am familiar with their behaviors overall. Thank you. 

I got my semi-feral to like me over a course of several months. What I did was give him lots of treats and canned food. He absolutely loves the Friskies Party Mix. I think it helped that he hung out with the cat next door, and that cat would come up to me and let me pet it. So my semi-feral started to get a little braver and slowly let me pet him over the course of a few months. His taming was slow...some days he didn't want anything to do with me and acted downright afraid. On these days I just left him alone. I also never approached him...he always had to approach me. Once he started to let me pet him, I started propping my front door open and putting a few treats just inside the door. Again, it helped that the neighbor's cat wandered right in my house like he owned the place. My semi-feral started coming in a little bit further each day, though if anything scared him he ran for the door. He also would not come in if the TV was on at first. The first time he got brave enough to come in while the TV was on, he just stopped and stared at the screen. He was completely mesmerized. Now he just ignores the TV. It probably took 6 weeks or more before he was ok with me shutting the door behind him. I knew I probably could shut the door when he got to the point that he was falling asleep in the house. What I did was slowly closed the door over an inch every day. Now my cat comes in at night and sleeps indoors, but he is still out during the day. He no longer seems to be afraid of me at all, though he is still cautious around my husband. Saturday is his first vet visit. I wish I could keep him in the house more, but I have one dog that really doesn't like cats. I am trying to work on her, but that too will definitely be a slow process. 

Yes, slow movements, soft voices and routine are the key.  If he's used to being on his own, he may take awhile to warm up.

Is there another room you can place him in alone?  One that has no furniture for him to hide behind/under.  A box or carrier is enough for him to feel safe and, of course, his litterbox and food station.

Wherever he is, you can go into the room and sit on the floor so you are at his level.  Read out loud or just talk softly to him, telling him about your day.  It will get him used to a human presence and voice.

Thank you for all your work!