I think you should read FREE TO SELL again. you have a caravan listing in the category for mobile caravans, with auction and buy it know. Vehicles including caravans are not FREE TO LIST.
You have the breakdown of fees which are listing fee £14.99 and BIN £5.99. which do not come to the £35 you say.
https://www.ebay.co.uk/help/selling/fees-credits-invoices/fees-selling-vehicles-ebay-motors?id=4127&...
You are shown fees BEFORE YOU LIST, you click on LIST WITH DISPLAYED FEES? Why did you continue if you thought it was free.
