The site on Kestrel Road, just off Gretton Road, was first broken into at some point between 3.30am and 9.30am on Sunday, February 7.
Offenders broke into the site and damaged machinery and stole tools and clothing, including a Makita 18V cordless drill, Husqvarna disc cutter and black North Face jacket.
The same site was broken into again on the evening of Wednesday, February 10, when a red pressure washer, blue pressure washer and blue generator were stolen.
Police would like to speak to anyone who may have witnessed these incidents or who may have any information regarding them.
They would also like to speak to anyone who may have been offered any of the items for sale.
Witnesses or anyone with information about this incident are asked to contact police on 101 or Crimestoppers anonymously on 0800 555111.