Small, portable, and ideal for infrequent use:

 

Lighters leave smoke marks, though, and can't be used in really tight spots like wiring up front panel indicators and switches. The catalytic butane tip burns clean and makes heat without smoke. Except when you test it on your arm hair.

 

Sometimes I use my soldering iron, sliding up an down the shrink tubing. If you don't have to shrink tubing very often, you don't have to spend a lot of money on it.

 

The hot air blast from the solder-sucker iron tip is easy to aim, works in tight places, nad does not take up much room. There is probably a similar device available currently from another source.