FEM constraints closed (assembly) models

[Jee-Bee]

I have running into a issue with FEM and part design/ step file assemblies

I have in the example a b box with a cover. and i want to create a constraint on the inside of the cover. then i run into one of this two problems:
When let it multiple bodies i'm able to create a constraint on the inside of the cover but i'm not able to make a mesh of all the objects.
When create a compount of all the bodies i'm unable to add a constraint on the inside of the cover (unamble to select or see this face solo) but i'm able to create a mesh of all of this.

Creating first the constraints and make a compount afterwards break the selected faces so don't works eighter...

Anybody tips or tricks how to resolve this?

[openBrain]

With the help of Selection View with Picked Objets, you can reach every face of the compound (even hidden once).

[Jee-Bee]

edit i dit something wrong