[Stiglr]

All that unwelding and welding isn't really necessary.

What I normally do to set up a texture map for a (fairly) complex object:

1) In one viewport, create a square or rectangle ( square if I need to create a perfectly square-dimensioned texture map); make sure it's big enough to visually give you room to place objects. Move it a considerable distance away from the model in any viewport, and offset it so you can avoid confusion later as you work with parts and copies of parts. Lock it (so you can see it but not select it). Enter wireframe mode.

2) Select a major part of my model; in my case, I'm building aircraft, so I'd select the fuselage or a wing as a "major" part. COPY it. (The idea is to leave the original model untouched, so as not to mistakenly ruin it while doing mapping).

3) Paste the copy and move it up "into" the locked rectangle. Rescale it to take up as much or as little space on the texture map as it "deserves"; in my example, the wings and fuselage would take up large %s of space, the inside of the wing root I would shrink down and wedge into space between major objects. Any objects that are to be contiguous, or that get a lot of visual scrutiny, I would scale them the same degree, to make things easier when painting. For example, I would not split up the top and bottom of a wing and size them differently.

To help in this process, I may need to move the copied parts "forward or backward" so that they can be seen "in front" of the guide rectangle, if I need to work outside of wireframe mode.

4) For surfaces that need to be rotated on axis or tilted for a more direct "camera angle", I would select the surfaces and Cut Away Object. Then, move, rotate or otherwise manipulate so as to preserve surface sides that should mate on "seams". There's no real need to "weld" the common vertices together. They just need to appear as "flat" as possible against the rectangle in the viewport you're using for the sizing rectangle to face.

5) Repeat 2-4 for all parts of the model. After you do this for a short time, you'll get used to detaching and reorienting faces for "box" shaped objects, globes, etc.

6) Once you've created and positioned all the shapes in your rectangle, go full screen for the viewport you've created the rectangle in; zoom in your viewport until you can just barely see the sides of the rectangle. Enter whatever mode best suits you for making a graphics guide (for example, I leave wireframe mode, so that surface edges are visible on my guide, which may help me while painting). You may need to move objects that are "behind" the sizing rectangle, and thus won't appear on the guide. Then take a screen grab of the rectangle area (and all the parts in front of it) using Clipping Tool, SnagIt, or whatever screengrab utility you may have. Take care to take a perfectly square grab. Eventually, you'll resize that screengrab to 1024 x 1024, or whatever "power of 2" size you need to work with.

After creating my guide, I usually try and get into Photoshop and create a guide layer with text to describe all the shapes, so I don't forget later. Also place any notes about orientation (e.g., this side faces forward on this part, or "this square-shaped surface is the front of a box-shaped object, this one is the left side" or which wing is port and which is starboard, which are the tops of the wings, which are bottoms, etc.