Harris was against the idea of camping out because he didn't relish the prospect of having to deal with rainy weather in the wild.
In Chapter Two, both George and Jerome proposed camping out, but Harris warned about the difficulties rainy weather would impose upon them. As a response, Jerome accused Harris of having "no poetry" and no desire to be "wild and free." Jerome's thought was that, roughing it out in the wild would fulfill some inherent masculine desire to conquer nature.
Meanwhile, Harris was not so easily convinced. For his part, Jerome began to articulate his friend's arguments against camping out. First, setting up a tent in rainy weather would be an ordeal. Then, after the project was finished (assuming it was successful), lighting up a wood fire would be next to impossible, considering the dampness in the atmosphere. A stove would have to do.
Next, one wouldn't be able to have an after-dinner smoke because the tobacco would be too damp. This would then lead the campers to drink copiously in order to comfort themselves. Of course, the resulting intoxication would induce strange nightmares during the night, and the next morning, all the campers would likely be ill-tempered and under the weather.
In the end, the three friends made a compromise. They would camp out in good weather and resort to staying at inns or hotels when it rained. Problem solved!