Bilbo did not have much time to explain his plan to the dwarves. He formed the plan on the spur of the moment, taking advantage of the opportunity that presented itself when the Elvish chief guard and butler drank themselves into a stupor. Bilbo stole the chief guard's keys. Then he let all the dwarves out of their cells and gathered them at Thorin's cell. So it was only when they had already trusted him enough to leave their cells, and were all gathered together in the dungeon passageway, that he explained to them that he intended to pack them into barrels.
They quickly went from being impressed at his resourcefulness to complaining about the plan.
[Bilbo's] fears were quite justified, for they did not like it one bit, and started grumbling loudly in spite of their danger.
"We shall be bruised and battered to pieces, and drowned too, for certain!" they muttered. "We though you had got some sensible notion, when you managed to get hold of the keys. This is a mad idea!"
"Very well!" said Bilbo very downcast, and also rather annoyed. "Come along back to your nice cells, and I will lock you all in again, and you can sit there comfortably and think of a better plan -- but I don't suppose I shall ever got hold of the keys again, even if I feel inclined to try."
That was too much for them, and they calmed down. In the end, of course, they had to just what Bilbo suggested ...
They complained again when Bilbo went to pack them in.
Thorin had given a lot of trouble, and turned and twisted in his tub and grumbled like a large dog in a small kennel; while Balin, who came last, made a great fuss about his air-holes and said he was stifling, even before the lid was on.