[Nazgulled]

I fixed my problem, not sure if it helps others or not but let us recapitulate what to do to make this work:

1) Place your weather fanart folders (00, 01, 02...) somewhere you like, ie: D:\Backdrops\Weather.

2) Open PM3.HD Home.xml and search for the "Skin.HasSetting(Home_Enable_Custom_Back_Weather)" string inside a "multiimage" control.

3) Add an <imagepath> tag with "D:\Backdrops\Weather\$INFO[Weather.FanartCode]" (without the quotes). And comment the <info> tag, this is what solved it for me. Save the file.

4) Open XBMC, go to skin settings and enable the custom weather backgrounds. There's not need to sepecify a folder here.

As an example, here's the default "multiimage" control on the PM3.HD default Home.xml file:

<control type="multiimage">
<posx>356</posx>
<posy>100</posy>
<width>924</width>
<height>520</height>
<info>Skin.String(Home_Custom_Back_Weather_Folder)</info>
<timeperimage>5000</timeperimage>
<randomize>true</randomize>
<fadetime>2000</fadetime>
<include>backgroundfade</include>
<visible>ControlGroup(9000).HasFocus(5)</visible>
<visible>Skin.HasSetting(Home_Enable_Custom_Back_Weather)</visible>
</control>

And here's the changes as explained above:

<control type="multiimage">
<posx>356</posx>
<posy>100</posy>
<width>924</width>
<height>520</height>
<imagepath>D:\Backdrops\Weather\$INFO[Weather.FanartCode]</imagepath>
<!--<info>Skin.String(Home_Custom_Back_Weather_Folder)</info>-->
<timeperimage>5000</timeperimage>
<randomize>true</randomize>
<fadetime>2000</fadetime>
<include>backgroundfade</include>
<visible>ControlGroup(9000).HasFocus(5)</visible>
<visible>Skin.HasSetting(Home_Enable_Custom_Back_Weather)</visible>
</control>

Note the bold lines...

This has worked for me I tried to understand what the <info> label does exactly but was not able too, but without it, it solved the problem for me.

Hopefully, this will help others having the same problem... What would be nice is to have proper support for this on the PM3.HD skin, without having the need to do manual changes to .xml files. This sucks because when we update XBMC, these changes will be overwritten