The question is what "stuff" are you talking about. If you have a lot of electronics or other items in their new boxes - you might be charged a duty. But we take everything out of its box and make sure that things look like they belong with the RV to prevent any questions.
If you have Christmas packages (gifts) I would avoid wrapping them because there are military checkpoints and they may want to see the contents of what you are bringing. But the military checkpoints are not concerned about duty - only checking for guns going south or drugs going north.
Our RV (5th wheel) has a nice flat panel TV, we carry three laptops, have our appliances, furniture and more and we never get asked to pay a duty. We do get asked if we are bringing alcohol or cigarettes for duty; guns or drugs by the military.
You should be fine unless you've got a lot of merchandise in nice pretty new boxes.
