So Im fairly convinced I know this but I´ll ask anyway.

Does River Blockade stack? I dont think so, but I´m hoping:D

It doesn't matter how many copies of River Blockade you have out - there is only 1 "first location effect triggered by an opponent each phase." The second attempt may end up being the first successful location effect, but it is still the second location effect triggered. So there is nothing for the location to actually stack on.

To be absolutely clear: there is no advantage in having more than one functioning River Blockade out (unless you have other cards that take advantage of Warship locations).

Thank you. Just as I thought.