You’d better look out David, or your family members will have to start locking their things away from you!
This yoga mat stuff seems to have very useful properties, if it is the same stuff I am thinking of. It appears to be a sheet of polyurethane rubber which, in liquid form (with solvents?) makes an incredibly strong, flexible and resilient glue. I don’t know anything about the chemistry of it, but it appears to be the same stuff which is used industrially to mount big engines on, between the engine and the concrete floor. I’ve not heard of it being used for marine engines, but I did once mount a little single cylinder Volvo Penta on some lumps of the industrial stuff, and as far as I could see it worked OK.
I once did a Hiab job on a yacht, whose owner told me he had bought (from The Warehouse) a cheap camping ground mat – same stuff as your wife’s yoga mat I think - and used it as a dry bedding for going between his chainplates and the ferrocement hull – bolted down extremely tight and the excess cut off – a quick, easy and cheap job which, on inspection a few years later, proved to have allowed no moisture to penetrate (often a problem with fc in this sort of detail). Its not cheap to buy in its industrial form, but if it’s the same stuff as used domestically it is relatively cheap and its amazing “memory” makes it potentially a material worth considering for a lot of applications besides fendering spars.
Maybe someone who knows more about these things can enlighten us with a bit more information.
PS
Leather, as you used on your boom jaws, is tougher of course. Good old-fashion leather- I read somewhere that the famous Fangio once ran a big-end bearing during a long-distance rally in Argentina - drained the oil and pulled off the sump on the side of the road and replaced the bearing shells with some pieces cut from his leather belt - and completed the race. I guess that toughness, and its ability to carry stiches, makes leather so good for fendering between oars and rowlocks as has been done probably for centuries.