We used
these. Festo 12V VUVG series solenoids are quite reliable and easy to mount compactly; we just stacked them together and put bolts through the mounting holes. They are pretty flat, so even if you don't mount them together, they will almost always fit somewhere.
As for preventing leaks, we just make sure to keep tubing away from anything sharp and make nice, smooth, 90 degree cuts when cutting tubing. Utility knives work well for this; the trick is to just push down, not saw. If you start with tanks pressurized, you can catch leaks before a match.