@Phil *****
There is no reason why you should not be tax resident in Thailand when you have DTV.
When you stay at least 180 days in a calendar year in Thailand, you are considered tax resident, even on tourist visa and visa exemption when you manage to stay that long, and also without a bank account you are still tax resident and money brought in might be taxable, depending on your situation.
That it is difficult to trace without a bank account does not change this fact, only might make it more easy to evade.