If you want to keep it in cash then just keep it in USD or GBP etc.
The reason why interest rates are so low (well there's a few reasons) is because the Bank of Thailand interest rate is only 1%. You can get fixed deposit saving accounts here but the rates are very low, like 0.5% per year.
The only place where I (or specifically my ex-wife) found I could get a decent 3-4% interest rate in cash savings here was when we were saving in the the government teacher's credit union system over here.
But again that necessitates being married to someone who works for the government and again the money wouldn't be in an account in your name.
Over here you're kind of limited to either
a. keep the cash abroad and transfer money over larger lump sums when the exchange rate is decent.
b. just buy gold if you want to save and invest long term over here.
c. keep your investments in the US
Each has their own risks attached to them of course.
Also just as a side note, I have nothing against Kasikorn, but 'generally' the easiest solutions that foreigners use to circumnavigate bureaucracy and rules etc etc tend to become the biggest problems 5 years later down the line. The Bangkok Bank fiasco being the obvious example, tightening tourist visa rules, and the stricter enforcement of needing
*******
k deposit for the Non-O visas and extensions being another.
It's always smart to have a couple of options and/or back-ups at the ready in case something happens.
Even my wife has 3 different bank accounts just in case there's a problem.