Heres a bracket designed for 30kg rated light duty swivel castors. 

Bracket is designed to fit to internal corners. 
If you intend to have the wheels flush or low to the inner skirt you're fitting to, i would recommend a 5mm spacer on both sides. 

Castor wheels plate: https://www.diy.com/departments/unbraked-light-duty-swivel-castor-dia-50mm-max-weight-30kg/5010952855462_BQ.prd

Any castor with a 50x50mm plate will work. 

Other hardware required:
Castor to bracket fixings - Note these can be halved if you only need 2 if fixing half bolts
x8 (M6x20 Bolts)
x6 (M6 Nuts)
x16 (M6 Washers)
Fixing Bracket to Cabinet/drawers/etc
x24 (4.5 x20mm Wood Screws) 

No supports needed for PLA, however if you choose other materials such as PETG or ASA I would recommend a support for the inset face where the castor fits.