I used the exact same stuff a year ago. My LY had plenty o' leaks around the same areas Phredd mentions.
I used a cheeze cloth material, ( I assume Fiberglass ) that was recommended by the manufacturer.
I applied a base coat of Kool Seal then mashed the cheeze cloth into the bed.
I followed up with two coats over that. I used a 6 " paint roller to apply the sealant. That made for much quicker and easier application as I had the roller connected to an extended paint pole, (no leaning over).
I am very pleased with the results, I have not seen any leaks over a year.
As for othe leak locations, The locations that the end caps meet the body over the cockpit windows and the end cap on the sides. I find this the most common on all LY's that I have seen.
When buying, open the rear cabinets and you can typically see that the end caps have been leaking and has effected the paneling inside of the cabinets.
Like Phredd, I cleaned with clorox solution and actually scrubbed the area. Mine had been sealed previously and the dirt had settled into the small undulations.