There are rack mount slide out trays available you can just plop a desktop case into...
Yes,
this may be a good candidate. You can actually add handles to it to make it rackmount compatible.

About this only thing missing is hot swappable bays (but that's not a necessity). Being aluminum built, it only weighs 6.8 kgs as well, so that's another plus. Even with the motherboard and six hard drives installed, I doubt it would weigh more than 10kg. That's about 50% less than most rackmount chassis weigh
without anything installed in them!