This layby is very popular with truckers so it can be messy, and you may not be able to get close at times.
You are looking for a magnetic key safe so bring your own pen.
It should be an easy find if you can park close. You don't need to cross any barriers or rummage around in any rubbish.
Congratulations to Witch24 for the First To Find
I am not particularly attached to these caches so if they are in the way of something more impressive please message me and I will retire them)