There has to be something that is making seats not last as long as the next person. Way to many things can be different. I am not a small guy at 240s, but my seat is new looking after 150+ hrs.
I guess some thoughts can be posted.
About me...
1... I now have my tractor under cover form the "Florida" sun. With that said, no winters to kill the seat, but the sun is just as bad.
2... "Before" it was under cover, I always had the seat flipped up (on the steering wheel) when not in use, this way rain, sun, dirt and so on would not get on the seating area.
3... I clean (rinse off) my tractor "almost" after every time I use it. So there isn't things being pushed into it, dirt and so on the next time I use it.
4... As far as I know my big butt sits right in the middle off the seat. So I am not leaning more to the left or right.
5... Again being in Florida, 95% of the time I am on the tractor wearing shorts and not heavy jeans and nothing in pockets.
I am sure there is more that can be said about this subject, but maybe my small list will point to something that is or not being done to have seat problems.