I've done two things: these are 2.5 inch drives, and they don't take much space and weigh little. finally, they have no moving parts.
at first, there are venting holes just between the 3.5 inch drive rack and the floppy/card reader. i screwed them directly to the case. this was satisfactory, but ugly.
then, i picked up a 5.25 inch rack that has space for 4 removable 2.5 inch sleds, and another that has space for 2x 2.5inch internal drives and a slot loading dvd writer.
so, my front rack has 6 x 2.5inch drives, one slot loading dvd writer, and in the 3.5 inch rack, a usb/sd/cf panel. the scsi to Sata converters are fairly small, but it is a bit cramped behind the 5.25 inch racks. short cables are important, and since everybody wants power, there are way too many Y splitters.
I can boot from the scsi devices, scsi-to-sata converters, and of course, from the on-board fiber channel.
fiber channel SSD's are available, but I'm not dropping 3 kilobucks on a 73GB drive.