I think it's safe as it can be Brad...
the pipe part of the Eheim goes in to the RC tank and used quite a bit of goop there
also filled the inside of the cover with conformal coating... and used goop for the round edge of the cover part, where it makes contact with the flat surface of the RC tank... i think you can use crazy glue here as well, didn't use it though... and finally sealed the external edge of the part with a bit of goop again... ahhh love the smell of the goop heh
OK here's what I did finally... actually sealing the outer edge seems not so important... hehe Una you may not need to use too much goop here
I made a slight opening with the screwdriver as shown in the pic below, and with the pump still running hold it from the tank in the air...
No leaks
BTW I don't take any responsibilities, whatsoever for the above said... If anybody wants to try this -you don't need to- try it at your own risk and don't blame me if anything goes wrong...
if anyone's worried about leaks procooling style is a better choice and requires less time to build...
Bruce