Mounting 2 regular HDD's that close together isn't a good idea. I know this from experience! Having never had any SSD's before I was wondering if heat is an issue at all? Is it okay to mount them that close together?
Some SSDs use more power as they use multiple controllers in RAID; for example the OCZ Apex and other low quality SSD.
But modern/normal SSDs would consume about 0,2W idle? That would mean you can put them against eachother and basically forget about heat altogether. As comparison a 7200rpm 3,5" drive uses about 6-8W to idle; up to 40 times more.