[allenphoon]

Well,if you think too much rain will make the media wet, then you can add in some media like coconut peat/chunck/fibre, pearlite, charcoal, burnt soil into the media instead using pure sphagnum moss,
If you concern that media like pearlite will flood out once the pot fill with rain or peat flow out from the pot through drainage hole in the pot, you can use sphagnum moss as a layer on top and bottom to keep them stay at there place, hope this will help you.

My humble opinion is that plants really do not need much care, they are much tolerant and stronger than what we think.