I looked into tankless water heaters a while back and decided against them. While they might save money in operating costs, I'm not sure that is ever offset by the higher initial cost. The other problems are, they can only raise the water temperature a certain amount based on the flow rate. They also need a certain flow rate to even operate. In a travel trailer, with a low flow shower head and faucets, I don't see how they would work properly.
My suggestion is to check the specifications for your unit and see what flow rate is required to trigger the burner and then check to see if you can achieve that rate of flow in your shower or any other location.
Here is what you should be looking for in your specifications:
Note that in this example, the minimum flow rate is 2.5-3 gallons per minute.