Hosts welcome different types of RVs. The stipulated maximum length refers to the space designated for your total length. If you have a travel trailer, for example, you will need to add your RV length + your tow vehicle together. If you are a Class A towing a toad, for another example, you would include both your toad + your RV. In this case, however, you can possibly detach your toad and park them separately.
Please make sure to read the Host's profiles about the length that they can accommodate and do not exceed their specification. Many times, other members mention the parking area and reference their RV length in some of the reviews that they write, which could also be helpful to read.