I pulled a 5X10 Uhaul
trailer from Chicago to Miami with a 67 beetle.
Yes , it was nuts but I didn't have any other choice.
I added an oil temp guage and found if I left the engine hood up it ran at normal temp at 55 mph.
I got passed by a farmer and his tractor crossing the Chatannoga mts.
And A big storm headwind stopped me dead in my tracks in Georgia, but I made it ok.
A year later I came back but with a 4x6 trailer, it was much easier.
Now the newer Beetle has much more power I wouldn't think a 13 footer would be too much of a problem, except maybe in the mountains.