If you can't be comfortable with a shower over which you have ZERO control, nicely decline the offer of a shower. A shower is a gift, and it's really only polite to give input when you're asked. That said, the MTB is usually consulted about the location, especially if it involves significant travel (like a 4 hour drive), the date, and the guest list.
With the guest list, first ask your hosts how many guests they can accommodate-you don't want to give a guest list of 50 people when they can only host 20. That's a good time to bring up a co-ed shower-but remember, your hosts have the final say, and because a shower is a gift, you can either accept what they're willing to give with a smile or turn down the shower altogether.
For location, it is not OK to request a specific location, but you can certainly point out considerations like your doctor not wanting you to travel more than an hour away after a certain date.
And unless you're asked for input about any other specific details, you should keep quiet, keep smiling, and be thankful for what you get. Good luck!