How can i show that my skid base frame established directly on the ground in physical modeler workflow?

Hello,

In the below SKID i need to show that the base frame is mounted directly on the ground. All the ground beams will be layed on the floor and on the 4  cornens i will use 4 fix points  How this can be applied on physical

modeler?

 

 Thank you in advance for your support.

Kind Regards,