I started soloing Tigers at 67 and landing Sleep was definitely a problem, even with capped enfeebling skill and an Enfeebling Torque (no merits) until level 69. At 67 you can also start doing Thunder 3 -> Aeroga 3 which should kill the Tiger if it doesn't resist.
Yeah, sleeps are annoying to land. For me, 65 is a pivotal level for this camp because it means torque (+7) and the final tier of skill merits (+2) along with the skill boost that comes naturally from leveling to 65 (+something). Even with all that, sleep accuracy is still not quite what I'd consider ideal, and that's with the full +16 from merits backing me up. One can imagine what it might be like before that, especially without merits.
Fortunately, by that level, you should be able to take the things out with two nukes if you do not get resisted (Blizzard 3 followed by Stonega 3 does just enough damage to take them out, although the exact nukes needed will obviously be different for everyone depending on just how well geared they are) meaning you will not even need to sleep it in most cases. The only other thing that could possibly go wrong is the tiger getting two double attacks in a row (ANNOYING) and hitting you through your 3 shadows before your second nuke fires.
The popular thing nowadays is to sync a manaburn to 62 and level off Tigers that way. I know several people that went from 62-75 doing that.
Yeah, this is what I do, only I tend to be more of a 1 man army as far as the manaburning goes and only use support in the form of Flash and Cures. If you sync down to 62-63 or so, definitely bring some assistance. Even with merits, my performance downright sucks at those levels >_>