Basically, ECU are designed without assuming that lid can open.
I contacted an senior engineer who has been working with a world-class electronics company for more than 20 years and his reply was quite simple and I like his solution.

After several tries, we decided to use 2 methods in order to close the lid after applying a little of thermal grease on dedicated location.
so we can make sure the protection from heat and no water damage.  

• Using silicon rubber sheet to close lid.

• Using silicon gun and replicate factory shape after removing factory silicon sealing.