hello,
I have completed undergraduate studies in plastic technology from Central Institute of Plastics Engineering and Technology INDIA,also i have successfully completed a project on design and development of a Power take over cover used in automotive tractors in SAME tractors INDIA.
that cover has a thread to fix it. so you have the problem with poor lid design of plastic container,
i am sure you must be using one of the following thermoplastic materials like PS(polystyrene), PP(polyproplyene) , PET (polyethylene terepthalate), HDPE (in rare case) to manufacture your product. Actually there is another way to rectify your problem apart from design change.
if you are interested, you can reply me or contact me through mobile, so that we can have discussion and i will provide the feed backs.
thanks