Well, there's no "right" way. Just choose the way, that fits you needs best.
I mixed the used ways of adding RenderPasses a bit through the testcases to make clear, that there is more than one way to do it.
I would suggest to use the "shortest" one for your specific case.
e.g.
BranchGroup scene = createScene();
env.addPerspectiveBranch( scene );
or
BranchGroup scene = createScene();
RenderPassConfig rpConf = doSomethingThatCreatesARenderPassConfig();
env.addBranchGraph( scene, rpConf );
or
BranchGroup scene = createScene();
RenderPass rp = doSomethingThatCreatesARenderPass( scene );
env.addRenderPass( rp );
You see, there are shorter methods, that do the same, if you have less parameters, that carry the same information.
Marvin