I've figured out a solution for upside down multi adapters, without docking ports.

[Galane]

It will require a multi-piece new part, but would result in a clean looking setup that can be staged normally.

As an example. Take one of the 1 to 4 adapters and flip it upside down. Next, cut it into 5 parts, one in the middle with a single node on the bottom and four around the sides, each with a single node on top. The side parts connect to the center part with the same style of non-node attachments as struts.

If they can be angled or use interlocking shapes (if that makes a difference in KSP physics) to resist coming apart under thrust, that'd be even better. Hold your left hand palm up, fingers curled up. That's the center part. Hold your right hand palm down and hook your fingers over your left hand's fingers as one of the side parts. Upward thrust on the center locks it to the side part.

The catch is an adapter like this would have to be assembled in the VAB, or loaded with the subassembly mod, but it wouldn't violate the tree structure, same as sticking things to the bottom of a 1-to-n adapter then connecting them with struts doesn't.

[Greys]

You would still have the problem that without docking ports you're not allowed to have branches in the tree structure come together, they can only branch further, so while it would appear to work, it really wouldn't do any more than flipping the multicoupler over. It would only be attached at one point and the rest would just happen to be in the same place, without being attached, like putting the tips of your fingers together, there's nothing to keep them from coming apart again.

[Galane]

Parts hanging off the bottom of a multi adapter can be connected with struts, so can more parts hanging from those parts. So why couldn't the parts like this be connected with strut type bonds?

[Greys]

struts are very different than everything, they don't even have normal physics and generally aren't considered a part, also they have to be placed on two points and the mesh will be manipulated based on those points; there's also ray casting involved.

If you want a part that doesn't look like a stick, struts are not the way to go about it. You're better off just using an upsidedown multicoupler and fixing the attachment with struts

[Tiron]

Parts hanging off the bottom of a multi adapter can be connected with struts, so can more parts hanging from those parts. So why couldn't the parts like this be connected with strut type bonds?

You mean like multidocking does with the 2nd and subsequent port pairs that lock together?

[shand]

Greys: my experience with struts is its not a two point so much as a point and a vector. this doesnt change what you are saying but making sure the OP gets the right info

I would like to see a second "docking port" type module that could solve this. maybe something like all attachment points are considered docking ports upon physics initalisation but switch to static attachment points upon launch (or docking ports unable to undock, or dock)? that would be a very messy way of doing it, but it could work. (second to that, if each large tank had 3 of these types of temporary docking port type nodes then you could get a 4 point attachment between large tanks - completely eliminating wobble.

Again a messy solution - but a solution non-the-less.

[Galane]

With the subassembly mod I assume a part could be pre-built with strut links (enough to make a very solid link) connecting the center and the two or more side pieces, with each side piece having a coupler or stack separator on top.

What I bet would still be an issue is no node connection from the center part to anything above it. Could have a node on one side to connect to one of side parts...

[Prophes0r]

There is a VERY easy way to do this with struts and hide them.

Step 1, attach your adapter, lets just call it a triple.

Step 2, attach 3 tanks (or whatever).

Step 3, attach the bottom adapter upside down.

Step 4, grab a strut, set symmetry to triple (because we used a 3 way splitter)

Step 5, maneuver your camera until it clips through one of your tanks, and face up. You should be looking at the attachment face for the top splitter. Attach the first part of the strut.

Step 6, turn the camera down, make sure it is still clipped through the tank. You should now be looking at the attachment points on the top side of the lower splitter. Attach the strut to this face. It should go straight through the tank.

Sometimes the strut will simply attach itself to the top side, and the top of the tank depending on the shape of your tank. In that case, repeat the steps from the bottom side to firmly attach both splitters to all 3 points. This can also be used to hide struts inside wing segments that clip together.