A few years ago one of my buddies and I did the entire interior of a Dodge Ram Charger in Herculiner. What a disappointment and waste of money that was! We spent a full weekend doing prep work then about died from the fumes while applying it. It smelled like horrendous sewer gas or something. To make it worse it did nothing for noise control or heat transfer then it badly flaked off in the cargo area and floor boards. I doubt our prep work was the reason it flaked off as we were very thorough in prepping and cleaning. We are just of the opinion Herculiner isn't that great of a product.
On the other hand, I had the interior of my truck Rhinolined about 3 year ago after doing some rust repair to the 30+ year old floor. I did it mainly for rust proofing and the hope of noise reduction. I personally do not feel bed liner alone is enough to keep heat and noise at bay in a closed cab vehicle you spend a lot of time in after what we learned on the Ram Charger so I also added DynaMat, some patches of jute then a very thick rubber floor mat over that. I normally do not like jute in an off-road rig where water intrusion often gets into the interior but with Rhino below the jute I wasn't worried about future floor board rusting issues. In the end, it cleans up easy, no worries of rust settling in under the DynaMa/Jute and extremely quiet for 70's vintage truck but I can't say I notice any difference either way with heat transfer because I didn't have heat transfer concerns before with carpet.
For off-roadster like a Jeep, Montero, etc. a quality professionally installed bedliner like Rhino, LineX, would probably be just fine bare but I wouldn't recommend any of the DIY out of the can liners....at least not Herculiner. That Al's stuff looks pretty promising though!
This is Rhinoliner
Rhinoliner with DynaMat, Jute and a heavy rubber mat over it. Its pretty dang quiet for an old truck