I removed the rear seats in my '99 Ford Supercab - they weigh a little, but also occupy a lot of the volume of the space even when down. In the '99, the seat back folds down leaving a level shelf.
I just removed the rear seats on my 2015 Ford Supercab, but there are some issues on the later model truck. I have the Lariat, which has a 60/40 seat and it folds up, not down. Under the 40 side behind the driver there is a subwoofer, it could be relocated to the rear wall but the wiring would have to be extended. After removing it all, I ended up putting the 40 side back in, it covers the subwoofer without much wasted space, and would allow carrying one passenger there if we ever did.
The seat back is a bit tricky to remove (there are three hidden spring clips that must be released). After removing it, I discovered that the flow through vents in the back of the cab allow in a substantial amount of wind/road noise whenever the flaps open - which is anytime the climate control fan is on. Verified by switching to recirculation, they snap shut and instantly the noise goes away. You do not hear it with the seat back in place because it acts as a baffle. On the '99, with nearly identical vents, the sound proofing on the back cab wall has sound baffling in it, also it is noisy enough maybe you just don't notice. I considered recreating the '99 sound baffling but in the end reinstalled the seat back. There are several other things behind it on the '15 that are not removable (rear window motor, middle seat shoulder belt tower) that the seat back also covers, so the volume taken by the seat back doesn't subtract as much as you thought. I ended up with only the 60% side seat bottom removed, which is a lot of space. You will have to find another place to put the jack and tire change tools which mount on the passenger side seat bracket.