I've never used this method before personally - BUT a quick plug for mckenziecz who has a proper arch roller for rental for £35... Everywhere else it's £80+.
Good last resort if you can't do it the cheaper way
Hardly surprising honestly. Mighty mods are more of a sketch show type affair when it comes to car mods. They will have done it all before camera and just given the sense of the methodology on film as an illustration.
You'd be better off renting mackenziecz's arch roller than to be faffing around with rubber tent mallets