Typically high tax countries︀ don't have DTAs with tax heavens. The UK is an exception though, as many tax︁ heavens are former protectorates / colonies of the UK (like the UAE).
I see the︂ UK even has a DTA with St Kitts and Nevis signed in 1948.
So if︃ you live in St Kitts, getting a local company and good banking for international business︄ seems very difficult. Instead a TNR UK Ltd would make sense I guess (or a︅ US LLC of course).