Quoted:
OdT, why wouldn't you designate 1 room, for the guys that just want to take a shit, shower and shave? $20 to get cleaned up isn't too bad....
There's just not enough volume to make it work.
Even in the RV park business where we attempted to cater to that customer, the coin operated showers cover the hot water, sewer, property tax, etc. There still wasn't enough traffic to make them much more than an inconvenience for normal business.
Cleaning the room is another constant cost. The payroll cost percentage would go through the roof by renting rooms for $20..... no matter how many minutes or hours the guest is in the room. Hence the main reason it just isn't realistic. (if someone rents you a room for $20, run like hell or double up on your vaccinations)
Gotta have volume to make it work. Especially with the cost of being on an interstate.
Truck stops, (like YOPD mentions), have enough volume to make it (showers) work. But it's more a service to draw customers in with. The money is in the sale of goods (fuel & junk food, I guess).