You can do it,
DISCLAIMER I'm not saying you SHOULD do it.
Paradoxically the stricter the country, the more lax the drug security. BUT if youre even transiting Singapore from Cambodia, youre fully security screened ON ARRIVAL at the gate.
In some of these countries sourcing internally may be better.
The hardest to source are Hong Kong (garbage on offer) and Japan, just forget even trying unless youre local.
Main tips: Most dudes who fail be looking like a cliche 'dopehead' cover extreme tattoo work. dress preppy, get a military haircut, you'll look a tool,.but you'll save yourself endless grief all over Asia at checkpoints. Stereotypes rule there. Or you can be the coolest inmate in an asian hellhole, your choice. Never check in your stash, carry it on your person, at least chest high. Dogs noses are amazing close up, and near useless 3 feet from target. Keep shit airtight. Dont pack things hidden inside other things, that will show on xrays and be a redflag. Know and keep below each paranoid prohibition regime's "trafficking" amounts. Hide things in plain sight. Eg place weed caps in a bottle rhat is commercially labeled as containing supplement caps. Avoid carrying 'paraphernalia' Edibles are a good option once youre safe across the frontiers, but be mindful the entire weight will be considered "drugs" if youre caught.
Most of my info is from google, some is personal experience, no matter, if you put in the time youll find an answer to almost any other related question. Proper planning prevents prohibitionist prison pain.