1. Portals only work when there are 2 portals in the world with the same tag. Third portal with same tag makes all 3 inactive untill you rename (or destroy) one of them.

2. You should build just one portal within your base and change it's tag every time you need to travel far. Risky, but cheap.

3. When you change portal's tag, dont jump in immediately - it takes 4-5 sec before it actually change it's tag. Otherwise you teleport to portal with tag you just replaced and wont be able to get back. Sorry for my eng.