I have used duplicolor paint for years and been very happy with it, didn't know they made a bedliner, I'll buy a can of that first and see how far it goes. I used to have a friend in the spray on business but i have 6 rigs to do right now and I can't ask for that much.....
You can buy a gallon of the Duplicolor liner for about $50 at Napa. I used it under my diamond plate panels to eliminate chafing and rust growth since I live in the PNW where that is a real concern. I do not recommend rolling this stuff on where you will see it, I'd make the extra effort to spray it.
I also saw the post about the ebay product, it looked very nice and I would recommend it from the pics posted by original poster. IIRC, it came with the needed spray gun also. Clean it well and you can use it again. I think you need a compressor though, keep that in mind.
I'd also recommend buying a tube of urethane from your paint shop (seems to be the only place I've found it is all) and seal any/all those pesky gaps much like you would use silicone and latex to seal up your house. Makes the finished turn out better and you don't have to hose it into the gaps to fill them, possibly compromising your overall finished look.
BTW, I have a Armacoat in my jeep and it's held up for 11 years so far. It's a line-x cousin that was considerably better than the squishy rhino product of the time. Rhino has since moved their formulation to be more like LineX, which is tough stuff. I think Armacoat is debunk now, have not seen it for a while. This was all before any of that DIY products were avaialable. For that matter, the 4wd hardware catalog looked like a brochure instead of a magazine back then too.
Regardless, it is one of the expensive spray on type you take to the shop to have done. I had my bare tub done, up the firewall and cowl, and also came over the bedrails. I also had the entire underside of the body and engine bay firewall done. Front fenders too, although, after 11 years of wheeling hard, they are no longer straight, but that's a differen topic, the liner under it is still nice and sound.