I know this question is not fully about Porches or Decks but it deals with in ground posts:

Is there an in ground sleeve that I can put into the ground to be able to slide the trellis out & in easier?

Background:
I have a decorative 3 sided wood screen/trellis that I have on the side of my house to shield a tankless water heater hung on side of house.

Trellis is installed in ground via 2 posts that holds the front panel. Side panel unscrews of the front 2 posts & only serves as balancers & side screening.

When doing maintenance on the tankless water heater, I can pull the posts out of the ground & the entire trellis can be removed for easier front access to the water heater.

However, getting the trellis posts back into the ground always is a chore & it doesn't go fully back into where it came out of...leaving about 3 inches of unpainted posts showing above ground.

I assume the trellis is fabricated with pressure treated wood 2x4's.

(sorry I don't have pictures handy at the moment to demonstrate.)