From personal experience stay away from duplicolor's bed armor. Herculiner is good but I agree with the spray on sentiment. The rattle cans don't do a great job in my experience, but if you thin it out herculiner you can use an air compressor and paint sprayer.
You CAN get even consistency with a roll on if you work at it though. I did the entire interior of my 72 scout and it looked pretty close to the Line-X job that I had done on the bed of my old tacoma (at less than 1/4 the cost). The big question is what's most important to you: the quality of the job done, the cost of the job, or your time? The job I did on the scout took north of 70 hours in prep and paint. The Line-X job cost around $500. If you want to try and take the easy way out it's just not going to look good or last.
If you wind up doing it be sure to read the instructions thoroughly, mask off the body line you want to follow and take pictures for us! Everybody loves a good write up of a garage project.