There isn't one easy climb (that I have found, anyway). There are several routes that you can take, but they all require you to to jump-climb from fence-top to low roof to pipes to higher ledge and so on. It is just a case of finding a route that you can manage.
If you really can't get up there, you could try reloading a game from before picking up the previous stash. Each stash location is randomly selected from the possible locations when you pick up the previous one, so picking that one up again might spawn the Bar stash in a different location.