My recommendation is 1 point fade (and pre reqs), 1 point mind blast (and pre reqs), 2-6 in shadow master (and pre reqs) depending on your +skills.
I really enjoyed my trapper, as she had 3 forms of decent damage (fire via fireblast, light via light sentry, physical via death sentry) and was very safe with ~ level 10 fade (after + skills), level 15 shadow master, and holy freeze merc. Hell was quite easy -- ancients were the only tough part due to continually getting cursed and having the lightning immune ancient always seem to step in and absorb my light sentry blasts.
Only downside is mf'ing. Unless you can afford enigma or can gamble/find an ammy with charges of teleport and resistances to switch out on meph runs, it is very slow going. I generally just stocked up on mf gear and ran lister/shenk/pindle over and over again. Those three are very fast and easy to run with a trapper.