The stick on diamond pattern bitumen from a UK classic car trim company called Woolies.
www.woolies-trim.co.uk £25 for 1.5mx 1.5m sheets, I used 3 sheets,heavy as hell and arrives on a big roll.
Plan was to sound deaden, tank and protect the new floor from any UK rain, if the carpets get wet I’d lift the carpet, the jute pre cut mats and mop the bitumen floor.
The second layer of shaped and pre cut tar/ felt mats are from SLS Germany and are expensive as hell when you buy the complete set ...which I did in a crazy moment.
Hopefully sound deadening qualities will be excellent, my own preference was a bitumen, felt, jute type underlay/ sound deadening over a modern silver foil type dynamat .
I may use the stick on bitumen in the doors as well as per original..ish