Since Riven's vendor is the only mod that has working mannequins for me (yes I tried the other two also) I have it installed in my game.  However, that mod hasn't been updated since 2011 and because Goodsprings has become modification central, the shop had huge landscape gaps and navmesh bugs plaguing it with all the different mods affecting Goodsprings also enabled.  Since I didn't find a fix anywhere I decided to roll up my sleeves, start up Geck and FNVedit and make one myself.

This mod fixes the landscape gaps and navmeshes when you have the mod Riven's vendor installed in addition to Children of the Wasteland and Lutana COTW expansion.  This patch also provides support for the modifications AWOP (A world of pain) and Vurt's Wasteland Flora Overhaul made to the Goodsprings area, but they aren't required for this patch to function, suffice to say is that if you have them, this patch will also fix the conflicts they have with Riven's shop, if you don't have them no problem, this won't break anything.
 
This patch will only fix all the gaps in the landscape if you have disabled the COTW shop in the Lutana COTW expansion MCM menu, leaving it enabled will still cause gaps to appear in front of the COTW shop although it will still be better than not using this patch. Fixing the landscape with both shops enabled can only be done by modifying both original mods which is way beyond the scope of this patch and since Lutana's mod provides the ability to disable the shop and place all the armors in an easy to use cabinet why bother leaving it enabled anyway? 

VERY IMPORTANT! Please place the .esp file that comes with this mod as low as possible in your load order, it should be loaded after all the above mentioned mods or it will not work!  Don't complain if you don't do this.

Note: Jessy, the vendor from Riven's shop will sometimes stroll a bit away from her shop, this is normal behaviour with the modified navmeshes, she will always stray back to her shop after a minute or two, so if you don't see her immediately just wait for a minute or two, she's close by and should appear shortly.