Make sure your teleporter exits don't deposit people facing a wall.
I usually set up my teleporter exits with their backs facing a wall, just in case some spy decides to get some funny ideas.
Also, when I play Engi the first thing that I do is drop a tele outside of the spawn room. Never know where you may want to set yp, and leaving a tele outside your base makes it to where you don't have to go back.
And building a sentry gun outside of your spawn room and carrying it to the front lines is a viable tactic if there aren't any metal crates near by. Just make sure to look out for spies.