IMHO you have made the right decision in sticking with the 18-135 and matching with a 10-18. I travelled to the UK and Europe in 2014 and took my 15mm fisheye, plus 24-105 on a full frame camera. In my case I was amost always using the wide end of the 24-105 or the fisheye. I didn't want for anything longer and the travel tripod I took was used just once during the whole 7 week period. If you can find one, a crowd filter would be invaluable....