Unless Barry is driving his nice Jaguar XJ-8, he almost always has some kind of hot rod or custom vehicle. I assume the producers of the show arrange those for him.
On the “storage wars is fake” thread awhile ago I had to do a search to see if Barry’s cars were his or not. Looks like he owns a bunch/most of them - and motorcyles. Seems Barry earned his millions in the grocery produce import/export business!
The episode with the Decoliner had the designer/builder (Grub) in it as well - so I imagine it was just on loan (good promo for Grub).
Here’s a link with some photos of Barry’s cars. Lots of annoying ads, but my software protection didn’t warn me of anything bad.
http://www.celebritycarsblog.com/celebrity/barry-weiss/