I have read the other post about the problems you are experiencing , you sure are having your share of bad luck. How old is the battery? I have read about people having problems with the power door and other things acting up because the battery voltage is low. A 5 year old battery is not worth keeping, I just replaced my battery in my other car this past summer, the battery was 4 years old and gave me no warning.
The P0300 mentions a lot of things to check and one of them is the coil packs (the things that provide the spark to the sparkplugs). If the battery was low your coil spark could be low and a misfire condition might occur.
I don't know for sure, I am just giving it my best guess. If the battery is old replacing it now before going on a trip is the best thing.
Keep us informed so that we can find out what's wrong in case our vans act up in the same way.