@Tim ******
There are two general times when you're asked for proof of funds
One is at a thai consulate when you're getting a visa for thailand (for a tourist visa many consulates require proof of 20K baht or the equivalent). In that instance you show a bank account (foreign or thai)
The other is when you're stamping into the country at passport control and in that instance (if you're asked) you have to show CASH either 20K baht or the equivalent.