No fancy workarounds that I know of - I merely do what was previously mentioned, which is paint in a 1:1 map, using the largest dimension of the 2:1 map for the size. Then after I'm done, throw it into PS and scale it to half the vertical size to get back to 2:1.
Is there a way to get MudBox to paint a 2:1 uv'ed FBX without having to scale up and down between 1:1 and 2:1? The reason why I like using MudBox is because I'm painting directly on a texture and my result is What I See Is What I Get. When you scale a texture horizontally from 2048 to 1024, you lose those pixels, and…
move the uvs to the second uv tile from 1-2... the only downside is that you cant cross the border line between the first and the second uv tile... afterwards you could merge the two textures in photoshop and scale the uvs back... have you tried to import a 2:1 texture as layer and paint on them..?