Though I've never seen a finished product or used it, I've read some good things about Al's Liner on other boards.
You can read about it and view a clip HERE
But honestly, it'll probably take you a good part of 4-5HRS from start to completion for something of this magantude, so from a time persepctive, you have to ask yourself is it worth it. Take your time, do some thorough research, have a little savy for it and pretty much everything will come out as anticipated. Alomst.
The prep work is tedious and can be really messy. Don't let the [heavily] edited time clip in the link above fool you. You also have to have the right environment [clean, spacious and well ventilated] to perform a top-notch job that rivals the professionals.... and you must be equiped with the right tools for the job.
Honestly, at the day's end, you may save a $100.00 at best - in comparison to what the professionals charge - but it's robbed you of several hours spent other more productive areas [family, work, play etc...].
I'd rather drop my truck off to a reputable company like Line-x [or equivalent], pick it up a few hours later, pay the little extra and have comprehensive nation-wide warranty coverage along with non-wasted several hours. Warranty is a big issue.
I read many years ago on a Toyota board of a guy who attempted his own spray in liner in his Tacoma. He was a career spray painter so had the savy, tools and environment for a proper job. Everything turned out real nice [I remeber the pictures he posted] for a few months. When the back corner of his spray-in liner started peeling a few months later, he contacted the manufacturer [I don't remember who it was] and tried to pursue the manufacturer's claims of "limited lifetime warranty." His claim was denied after several email exchanges. Why? They claimed operated error during the application process. Think about it....
Like I said earlier, the potential headbucks are not worth saving a few $$$'s for.
I'm all for DIY attempts in just about every facet in life, but in this instance, I say get it done professionally.