Just got this reply this morning:

What worries me a bit is "directly at check-in counter"
My experience is you can not pay clerks at check in counter, they will weight your luggage and make a note to pay at their ticketing desk, then come back to check in.Theoretically I have 115 minutes between flights (I land from biz with fast track and usually am at check in 30 min after landing) Unless flight is late I will be OK, dunno for you Nightbus!

Thank you for your query regarding extra baggage. Please be informed that baggage carried in excess of the free baggage allowance is charged as follows, irrespective of the class paid for and used by the passenger. You may purchase the excess baggage directly at the check-in counter on your departure date.


Between Bangkok and THB Per Kilogram
Khon Kaen/ Udon Thani 55
Chiang Mai/ Ubon Ratchathani 60
Surat Thani 65
Chiang Rai/ Phuket/ Krabi 70
Hat Yai 80
Between Chiang Mai​ and Phuket 125

*Remark: Excess Baggage Charge rates are included VAT 7%.
Should you need further information, please do not hesitate to contact us.

Also curious with my ROP silver status, doubt I will get the extra 10 kg.

Bangkok Airways at UTH did print my QR BKK boarding pass and checked luggage through and passed immigration desk at UTH, and they allow 30kg if you join their FF program.