Your question is about moulding - yes silicone mold and resin a great answer.
BUT - why not redraw/design to the length you need - cut it in architectural foam - add a coating and have the length you need? Looks similar to some tiles and backsplash inserts I've seen around. Or, maybe you have some other use in mind.
Best of luck
:cheers: Jim
Experience is the BEST Teacher. Is that why it usually arrives in a shower of sparks, flash of light, loud bang, a cloud of smoke, AND -- a BILL to pay? You usually get it -- just after you need it.