My Speedie is a CMC with the thick gel coat finish. The tarp and duct tape (blue tape ok) was not a good idea BUT I was moving and Speedie was full of stuff for move. I had to use goo gone on duct tape and polishing compound to remove chaff marks - it would have been worse on a painted surface. If the tonneau had been mounted with snaps I would have gone that route instead of a tarp.
I've pulled with a Toyota 4 RNR too. I used an adjustable drop hitch receiver to keep the tow bar parallel with the ground --- same when pulling with Camry where it had to be raised a bit. You should not back towing with a VW tow bar. My 4 RNR has extended OEM mud guards. You could add mud flaps, add a removeable vinyl bra or an invisible 3M/XPEL bra. Avoid towing with snow on ground or even when raining as that kicks up grit.
Let me know if you head to my neck of the woods or need tourist info. Lots of IN, MI and WI expats here.