I made all of the connections in my system with soft silicone tubing from McMaster Carr. I used their part# 5236K891, and costs $1.15 / ft. It seems a small price to pay for peace of mind. It was a gentle fit over the glass nipples on the laser tube, and I added small tie wraps to be safe. It is transparent blue, looks nice, and will likely outlast many laser tubes without hardening or breaking down.
I did use great care with the routing of the tubing to ensure there weren't any bends that would lead to kinking. I maintained at least a 1.5 - 2" bend radius, and have not had any problems.