Certainly depends on soil and climate...
The resin may not rot, but stuff inside will get damp and rot.
If the ground settles, the resin will twist and bind the doors etc.
If you put it on a base, make sure that water can't get in from the bottom
edges and rust the stuff inside.
My ground was sloped, so I put cinder blocks at the corners and center
2x4 frame on top of that. Plywood on top of that. Flashing to keep
rain out of the wood and inside.
Problem was that I couldn't keep critters from making a home underneath.
Tried to close it off, but they just dug deeper...then died...then the flies
came.
Finally had to raise it higher so there was no way they could hide
under there.