Marine carpet isn't going to do jack to combat heat or sound. Far too many people equate "marine" with "better", and that's often just not the case. It's designed for a completely different environment, with very different needs of chosen materials, and different design of the vehicle. Biggest one is that boat decks are designed with drainage in mind, so that even when subjected to a downpour or waves crashing over the deck, the water won't pool on deck and sit.
Your truck floor isn't designed to do this, and pulling floor pan plugs or drilling holes in the tub isn't even close to the same thing.
All that said, I have run one of my old Scouts with carpet and topless...it wasn't horrible, but I also live in the Phoenix valley of Arizona where rain is uncommon. Even when it did rain, it usually is quick and followed by sun which evaporates the water out pretty quick. But it also required me to vacuum/blow it out FREQUENTLY. As in about every other day when I was daily driving it, because it was was like a dust/dirt magnet. Of course, living in a sandbox contributes to that quite a bit.
It ultimately was just a maintenance nightmare, and ironically, the driving force was sound control. Yet I completely forgot to consider wind, tire, and exhaust noise...which frankly, was deafening all on their own, and blocking what little sound came through the floor boards was pretty silly.