Jeanette,
My apologies.
To have you worry was not my intent.
Yes, in theory, you can avoid condensation issues with proper ventilation.
The key is "proper".
Teardrops as opposed to travel trailers have less condensation issues because the cooking is done outside.
However, as you are aware, just being alive creates a huge amount of warm moist air.
The general humidity levels do have an impact, but when dealing with such a small space, they really can't be counted on.
A few degrees difference is all it takes for warm moist air to condensate on a cooler surface, and as you can fast understand, warm sleeping/exhaling bodies can quickly raise the temperature and humidity level in a tear.
All is not lost, just keep the ventilation a high priority and you will be fine.
Some teardrops do not have a vapor barrier because the builder did not know about them, did not care, or felt it wasn't needed.
Some are constructed with open framing, and thus do not need one.
With no offense or harm meant to anyone, it must be realized that the vast majority of people building teardrops are not professional home builders...
Then on the other hand, a lot of brand new RV's roll off the assembly line destined to have water issues within a year...
Anyway, there is no set in stone way/method that one must follow to build a tear.
The exchange of information from this vast pool of experts is what makes the board concept so great, everyone is really good at something, and is willing to share.
My intent was to provide information to help you decide which route may be best for you.
Rigid foam in itself makes a pretty good vapor barrier...
if you seal all the voids.
Keep a window or vent partly open when occupying the tear, and "air it out" in the morning.
Remember that wood can get wet and not be damaged...as long as it can dry quickly.
(The wood hidden behind walls with no air movement stays damp...)
I think you'll be fine with your current plan, after all, you realize the importance of proper ventilation!
Rob