Welcome to the world of Shiba Inu's. Our Yugi is 9 years old and is and has been exactly as you described. She loves camping, getting into the truck for trips but when we get going a whole different story. Not making a big deal of things helps but in talking to several other Shiba owners in our area several are the same and looking on some of the online forums it is in their nature so don't sweat it. They are a different dog for those that have never had one and even at the big dog shows they say they are challenging as they have their own mind and agenda and are hard to trainin most cases.
Personally my dog is a lab/golden retriever cross and is everything that is wanted in a dog fro travel and camping. The wifes Shiba is,has and always will be special in that dept. and is a topic of a lot of conversations because of it. Do some reading on Shiba's and you can find a lot of this type of info online. If it were my lab I may be concerned but in a Shiba just do what you can and not worry about it.