Ahh, so it seems my problems with the dds were somehow related to me using the template.psd provided with the tutorial, if I just start from scratch it seems to work just fine:
Settings for exporting maps:
Compression: BC1 / DXT1
Format: RGBA8 (You have to select this before choosing the Compression)
Save: Selected layer (This is the reason why you need to combine all visible layers before exporting)
Mipmaps: No mipmaps
On occasion the map can look off after a message that multiple alpha layers have been combined during exporting. Just export the file to *.bmp (lossless fileformat that removes all alpha information on saving) and then just open that and export it again as *.dds.
If I can confirm these finding over time I'll make a post of how to use gimp for the maps as I guess many people might be put off by the barrier of the steep price of photoshop just to make maps for a game, especially when there is a free alternative.
P.s.: If the export is not a map but an icon file then you should choose no compression and use mipmaps.
Last edited by Pijotre : 12-22-2018 at 08:52 AM.