If you are planning to be away for a long trip (possibly a year or longer), do you need to have domestic health insurance with the ACA requirement? Or would your travel medical insurance be enough?
U.S. citizens living in a foreign country for at least 330 days of a 12-month period are not required to get health insurance coverage for that 12-month period. If you're uninsured and living abroad under this definition, you qualify for a health insurance exemption for plan years 2018 and earlier. This means you don’t have to pay the fee that other uninsured people must pay when they file their taxes.
Note: Starting with the 2019 plan year (for which you’ll file taxes in April 2020), the fee no longer applies. If you don’t have coverage during 2019 or later, you don’t need an exemption in order to avoid the penalty.
So for this year, if you're out of the country for at least 11 months, you don't need health insurance under the ACA. Starting next year, the ACA insurance requirement has been eliminated, so there is no penalty for not obtaining health insurance.