How do I put a craft or probe into a cargo bay?

[Klapaucius]

Oddly, after all these months, I still don't know how to do this.

 

I've got a seaplane with a cargo bay.  I've got a little boat I want to put inside it, and I put a docking port on the boat to hold it in place.  How do I do that?  I can't open the boat and make it a subassembly because KSP won't accept an entire craft with a root part as a subassembly.  How do I get the boat, which I built and tested separately into my plane?

 

I could load one on the runway, drive it off to the side, then launch the plane, switch and drive the boat into the bay, but that seems clunky. It also means I cannot upload it as a unit if I want to share it.

Edited June 17, 2018 by Klapaucius

[4x4cheesecake]

11 minutes ago, Klapaucius said:

KSP won't accept an entire craft with a root part as a subassembly

Just 'dock' an additional docking port to the one you want to use to hold the boat in place inside of the cargo bay. Re-root the craft to this additional docking port and you can pick up everything else to save it as subassembly.

You can also use the 'merge' option when you open a craft in the editor. This requires two separate crafts (seaplane & boat). Make sure that the docking ports of both crafts are the root part. This is important! If this is done, just open the seaplane in the editor, click 'open craft' again and look for your boat but instead of loading the boat, you choose the 'merge' option. You can place the boat now to the docking port like you would do with an sub-assembly.

[Xd the great]

Or build the boat in the plane.

Or add a docking port and a radial attachment point on your boat, add a useless piece in front of the port, set the useless piece as root, add stuff as subassembly.

Or use the merge craft function.