hah hah
halon and smoke detector? thats funny.
I mean seriously, the likelihood of a fire is very unlikely. I've splash water lots of time on my plugs and it always trip my ELCB without fail. (I not suggesting that splashing water is good!) Like I said before, I'm most likely just paranoid so you can always forget my comments. I'm just trying to say that the choice of materials used will defeat the reason for using PSB approved electrical plugs/outlets which are all made of fire retardant materials. Those commercial spray cover with the PSB sticker (quite costly) are most definitely fire retardant too. If you have any damaged PSB approved plugs, you can try to use a lighter on them. It will melt, turn black but most definitely will not catch fire.
In summary, no, I do not have any real solution as well except to use commercial spray covers instead of DIY. Those outdoor electrical boxes are available in Sim Lim Tower as well. Its waterproof and fire retardant as well but definitely cost an arm and leg. If not, IMVHO, I would not use those plastic boxes to DIY. Our ELCB is pretty decent at doing its job.
I hope you will not be offended, just my 2 cents.