I had the Thai and ASEAN airpasses with AirAsia and flew all over during the past 3 years, mostly Thailand, Indonesia, and Philippines. I didn't have a huge backpack but it was def bigger than the 7kg they allow. I never had my bag weighed at the gate. I recall once getting my daypack weighed at checkin but not the bigger one for some reason. They dont seem to see backpacks tho, or perhaps imagine they are quite light.

My strategy is simple: avoid the checkin desk by checking in online. This can be tough internationally but like a previous poster said, in Bali you can do it easily. But Ive had to do counter checkins plenty of times and they dont even give me a glance,

I dont even worry about it anymore, I figure if I get caught once a year (and have to pay the lastminute fee)I will still come out way ahead. The only time Ive seen crazy weighing was in the Philippines on a small island puddlejumper prop plane, and that was presumably for safety.