I would recommend the use of a _dedicated_ laminar flow cabinet for RNA work (isolation, setting up reverse transcription reactions) if possible. As Casadei says, don't underestimate RNases, but be careful not to underestimate the chance of contamination, either, by things ranging from plasmids to pollen.
Avoiding RNAse contamination is a multilayered task, that starts with a tidy lab and established routines, for keeping a low level of exogenous RNAses. Be aware that human skin is a source of exogenous RNAses, so avoid contact of hands and arms skin with surfaces and apparels in general. You can use a dedicated laminar flow or even a bench surface, if the throughput of RNA isolation in your lab is high. The important thing is that the surface, pippettes and plasticwares were only used for RNA procedures and scrupulously cleaned, before and after procedures (rubbing with 70% isopropanol in DEPC-treated water, followed by DEPC-water), and with bleaching every 5-7 days. You can also treat your surfaces with some commercial surfactant reagents (for instance RNAse away or similar) which actually are based on sodium hydroxide solutions . Remember, DEPC treatment is simply a means by which potential contaminating RNAses are inactivated, but it does not prevent further contamination, so maintain yours in a fridge or as freezed smaller aliquots. For endogenous RNAses, work quickly, and keep your reagents on ice or at 4C. Hope to have been useful.