From what i’ve searched the ThinkCentre M700 SFF or some ThinkStations might have 3x 2.5" SATA bays for HDDs/SSDs, but it’s hard to find documentation.
Basically i need a reliable box, small form factor (as possible), to shove 3 drives in and use as remote backup.
Does anyone have experience on any suitable models?

I have a Thinkcentre M75s Gen 2. It has 3 SATA ports, a 2.5" bay and a 3.5" bay. There are adapters available to mount a pair of 2.5" drives in a 3.5" bay. You will probably have to buy one of the custom SATA power cables for it since they usually only come with a cable for one drive.
Appreciated