klargester manhole cover install

[jackg]

Got to replace the manhole cover over an old klargester.
The old one was rusted as if the fumes from the klargester caused the rust.
I am going to use 3:1 mortar, but this does not seem to last. tends to crumble away.
Thought about using adhesive but it wont stick to the polypropylene base of the manhole cover.
Also considered screwing the base as well as mortar.
Any thoughts or suggestions if there are better ways?

 

[lostinthelight]

https://tarmac-bluecircle.co.uk/product/sulfacrete-trade/

 

[Ian H]

How about a thicker base and bringing it up and over the angled sides on the plastic part?