The future progressive tense is used when expressing events and action in progress at some future point, however the example sentence cannot be understood in that way.
走行中の箱乗りはご遠慮下さい!
Please don't lean out of the window when we're moving.
旅行中楽しい思いをした。
I had a good time during the trip.
旅行中ローマへ行きましたか。
Did you go to Rome during your travels?
旅行中はほとんど米は食べられなかった。
We were able to eat little rice during the tour.
旅行中の天気はどうだったかとビルにたずねた。
I asked Bill what the weather had been like during his travel.
旅行中に葉書を出すのは好きではない。
I don't like to send postcards when I'm on a trip.
旅行中に私はひどい風邪にかかった。
旅行中に雨が三回降った。
It rained three times during the trip.
旅行中に2、3日雨が降ることを考慮に入れておくといい。
You should allow for a few rainy days on your trip.
旅行中、ジョンと私は交替で車を運転した。
During the trip, John and I alternated driving the car.
歩行中にかばんから目を離さないように。
Keep an eye on your bag while walking.
父は海外旅行中です。
My father is now traveling abroad.
彼女は旅行中に撮ったスナップを見せてくれた。
She showed me the snaps which she had taken during her journey.
彼女は旅行中なくした指輪を見つけた。
She found the ring that she had lost during the journey.
彼は旅行中に病気になった。
He got sick during the trip.
彼は旅行中に見た人や物について話した。
He spoke of the people and the things that he had seen during his trip.