The Blizzard 1230-IV @ 50Mhz is indeed very hot. Towards the latter
years of Amiga Format I remember the '030 boards starting to appear in
40Mhz versions - possibly due to lower heat output. A lot had
heatsinks on them too.
I think it's perfectly safe to run it with the trapdoor on as the
European climate is a lot cooler. In the summer I would suggest
keeping it on a desk (not on the carpet etc) and give your Amiga
plenty of room (no magazines on top of the cooling outlets on top).
Remember that CPU intensive games will run the '030 at maximum power
for long periods of time so it will get as hot as it's allowed. In
this weather I would say try getting hold of a mini fan and putting it
inside the case somewhere to vent out warm air. I think these fans can
be found in PC shops from old GFX cards and CPUs, you might find a way
to obtain power by splicing the voltage from the floppy power
connector.
Ask for advice before doing this though.
Alternatively, just get a desk fan and blow air over your beloved
Amiga setup, it'll cool you down and possibly give more reliable
performance for your mid-summer gaming!