If you use the trapdoor cover with the CPU card you can start by replacing it with something that gives more airflow (I used the metal mech of some speakers for my A1200, gives both good airflow and still gives protection to the card).
A realy lowprofile 486/P1/videocard heatsink will do (then you might come away with not having to add extra height to the case).
On the other hand... I've had a Blizzard1230 running almost 24/7 with trapdoor on and no extra cooling without issues for years, so might just be a comfort of the mind thing.
