As far as I know, poppers are illegal as a recreational drug in all countries. The extent of prosecution varies, in Thailand they are openly on sale in gay online dating. I have traveled all countries you mentioned, and only once in over 20 flights in SEAsia had a cursory search of my hold luggage (on arrival inTaipei). I would search on internet (there might be no hits for this very specific case) and assess the risk. Or ask local gays about the extent of prosecution, but being caught with poppers at immigration might be very different.