Capital gains tax on investment income

[cross posted to the two country specific boards, but helpful to get a wider opinion also]

I have a relatively substantial ISA, a form of investment account that is tax exempt in the UK. I'm not required to pay CGT when I buy & sell investments within the account, and do not pay income tax when I withdraw funds.

I am considering relocating overseas, possibly to Portugal or Costa Rica. I will take-up specialist tax advice at the point when plans mature, but currently am just at the stage of early research, so wonder if members of this community might be able to provide some advice on the tax treatment of my investment account in each of the countries under consideration, if I were to become tax resident there.

From the somewhat limited information I'm able to find online:

Portugal - I would be required to pay CGT on profits from sale of stock within the account, and the Non-Habitual Resident scheme would not provide any relief for this type of investment income.

Costa Rica - I would only be liable for income or capital gains within the country, so my UK account would remain entirely tax free.

Have I understood this correctly in each case? In Portugal, are there any authorised mechanisms for preserving the tax efficiency I'm currently benefiting from by remaining a UK resident?

If this is not possible in either of my preferred locations, are there any other countries that might treat the investment account more favourably?

Many thanks in advance for any insight or suggestions.

Luke