The same way most of us do, with a measuring tape!!
Sorry, couldn't resist that. The length of the site is stated. If you want to keep your tow vehicle hooked up or sitting underneath the RV, you will need to find a site that is as long as your entire setup. We usually find a site that will fit our fifth wheel and then park our truck alongside.
If the website lists the site measurements, that is even better.
Get the site that will closest fit your needs. No reason to get a huge site, leave that for someone that NEEDS it.
We have a 35' fifth wheel and usually get a site that is around 50 feet, if possible.
