19% is tough, but you can prepare for them adequately on a trainer. I have a climb with a nasty 19% section in it that's short but nasty. (The rest of the climb is significant - takes a decent rider an hour to get to the top with nearly no descent.) I have a powermeter, so I know how much power it takes for me to get up that 19% - to keep moving at a snail's pace, it's about 300 watts, and to actually roll faster than that is 350+. So a good amount of power, but certainly well within the range of trainer - lots of guys do 2 x 20' sets at 300 watts. A trainer works fine for those steep climbs but you do have to work pretty hard on the trainer - it'll hurt.