When I was playing with the mod, I wasn't able to figure out how to attach tanks to all positions of the 4x Storage part without them looking wonky.

My solution was to add node_stack_b = -0.55, 0, 0.55, 0, 0, 1, 1 to each of the tank parts.

It needs more tweaking to get it to look just right, but this is the result. I'm not sure exactly what values to use for the position because I'm unfamiliar with editing models and modding in general. It takes a while to restart KSP each time to test them.

It's possible that I'm missing something in the vehicle editor or I've completely missed how these parts are supposed to work.

Hmm, the attachment nodes on this part should be in a way so that the container all fit neatly inside them...I will review that and post screenshots in the case they are there and you missed something ;-)

Closing this one. Just verified that the parts can be added in all orientation to make them fit symmetrically into the 4x Storge part without any modifications to the stack nodes.
If they should still cause troube, please re-open.