Oh yes, I have done these things, she has her dog bed in there and has treats in and out, Yes she is young but there is a narrow window of socialisation which tapers sharply after 16 weeks of age so time is of the essence, I am considering a small radio which is always on at home so she feels normal, the bark (last ride only) I feel was her saying "Oi, pay attention I'm being ignored in here".
The whirring of a rear mech is not a natural sound to a dog/puppy and let's face it she isn't far behind, I have had dogs for 40 plus years but even so this is new to me so all feed back/contribution welcome. First thing I did when I knew I was allowed another dog (wife a cat person) was buy a puppy training book to bring me up to date.
She is an outward going little girl so I feel I/we can do this.
At home when I get the trailer out she jumps in playing and chewing buckles etc so she isn't frightened of it in fact nothing seems to faze her at all, even an emergency siren just made her look up at me and I reassured he saying "tis only noise" and gave her a cuddle and off we toddled again, brilliant wee dog.