Permanent teleportation circles are for creating "custom" teleport destinations, such as a party's home base. Permanent teleportation circles themselves are only destinations, as you said. They don't allow you to teleport from them without casting the Teleportation Circle spell.
Yes
The spell says:
As you cast the spell, you draw a 10-foot-diameter circle on the ground inscribed with sigils that link your location to a permanent teleportation circle of your choice whose sigil sequence you know and that is on the same plane of existence as you.
D&D 5e co-creator Jeremy Crawford clarified on Twitter that the destination of teleport (which may be a sigil from teleportation circle) may move. At the time of the post tweets were considered official rulings by WotC (which is no longer the case):
The teleport spell requires a destination. The nature of that place isn't specified. It can be the deck of a moving ship, for instance.
Likewise, the surface of the circle is important, not its point in space. So, the surface may also move while performing the teleportation circle spell every day for a year, and after it has become permanent. It has no restrictions that the permanent sigil doesn't move:
When you cast teleportation circle, you create the circle on the ground. The circle is bound to that surface, not to a point in space.
What happens if I cast the spell on the vehicle for a year (and it is unmoving), and then the vehicle moves? Can it still be used as a destination point?
Yes, the target is the sigil, not the point in space the spell was cast.
Can I create a permanent TC on the vehicle if it is never in the same place twice in the first place?
Yes. Jeremy's post shows that.
But, even more from a real world perspective, all motion is relative. On Earth, we tend to think of places we travel to as stationary -- but they are not. They are rotating around the Earth's axis and revolving around the sun. To the car/planes we travel in, they are standing still (relative to themselves) and Earth is moving beneath them...
Alright, I'm getting too much into Einstein on a D&D question. I read "same location" more like "same spot" than the same longitude and latitude.
Best Answer
The verbiage "Until Dispelled" and "Permanent" are functionally the same with regards to spell duration.
As Jeremy Crawford indicates here.
Later this makes it into the official Sage Advice Compendium
So unless a spell description says otherwise it is still an effect of the spell and dispel magic ends spells.
The logic behind RAW as I see it is that dispel magic ends spells. A spell effect that becomes permanent is still an effect created by a spell, thus can be ended with dispel magic unless more specific verbiage (e.g. the text of a specific spell) states otherwise.