nickag wrote:
...My LBS also told me to mount the tyre when the last layer of glue was wet as it allowed to tyre to be centred on the rim before the glue dries.
+1 on this, install the tire with the final mounting coat (rim only) still wet. Stretch the tire equally out and down starting from the valve (with the wheel in a truing stand or trainer) and really stretch as you go so there's enough slack to lift the final bit up and over with just your fingers and thumbs. Then very quickly pinch, lift, and center the tire again with just a finger/thumb grip working all the way around from valve hole back to valve hole. Spin to check and you should be good to go.
It's strange to have trouble remounting a tire that's already been ridden but sometimes the first base tape layer can shrink up a lot making the tire much tighter. If that's the case then after the base tape layer has dried overnight restretch the glued tire on a clean rim for a few hours or more before tackling the final mounting job. That and practice dry mounting the tire a few times till you get the sequence and motion dialed and then do the final wet mount.
-Dave