I'd like to suggest a slightly diferent approach to the ladders you carry.
Werner makes a 2-ft "mechanics" type ladder- the type with steps on both sides. Not only does this ladder come in handy for climbing on my truck- the side rails form a "v-block" when open, making it real handy for cutting strut or pipe.
Werner also makes a 300# rated ladder that is either a 7 ft stepladder, or extension ladder to 14 ft. You probably have seen this ladder in use by your local cable or phone company. This ladder is my real workhorse.
For a real extension ladder, a 20 ft (or 24 ft) is used pretty often.
Finally, I use my 10 ft stepladder more often that I ever expected.
For getting on to sloped roofs, my 16 ft "4-way" ladder is a dream. By having the top portion horizontal, the base of the ladder rests against the roof, and not the gutter.
The last three ladders are not usually on the truck- but are well worth having.
