When it comes to low and slow on the Weber Kettle you need to ignore what they tell you in the Weber manual. By using good quality briquettes in a minion or snake arrangement you can keep the cooking temperature at a steady 110-120 C (230 - 250 F) for 6 or 7 hours with minimum attention.
Below are photos from a comparison I did recently between different types of briquettes.
By keeping tho top vent 3/4 closed and the bottom vent slightly cracked open you can keep the internal temperature very low and stable. Here is the heat profiles taken with my temperature logger for the 6+ hours of the test.
You can also use an automatic temperature controller to take away the manual maintenance. I use an IQ-110 when I want to be completely hands-off
The Weber Kettle is a very versatile unit.