You get to profit from my pain Tito...
If you try to use the default OOTB teamsite-like masterpage (default.master) on a search template, you get all types of errors.
You need to base your custom masterpage off out minimal.master. Try not to modify the original minimal.master. Make a copy of minimal.master, then add your custom HTML, JS, CSS and SharePoint placeholders to the copy.
Afterwards, goto Site Settings, and set your custom minimal.master copy as the custom masterpage for the search center.