The cache is a black small tube and magnetic and is outside the temple complex.
About Wat Tha Mai I, difficult to explain you have to see it with your own eyes. It is located near the Ping River and build in 1916.
Some more info on: http://www.lannatalkkhongdee.com/templeDetail.php?id=Temp0800040
Va n ubyr orgjrra gur pneg jurryf.