Keep cover from sagging over the bed

[barmanvarn]

I'm do a (very) slow resto on my Dad's old '69 C15.

When I'm not working on it, it sits next to the shop and it's only protection from the elements is a truck cover. While it's sat out like this, the bed has taken the brunt of the damage from the elements so the rust is getting pretty bad there.

The issue is mostly due to too much water getting into the bed because the cover sags and collects water.

So I'm looking for a cheap, simple way to keep the cover from sagging over in the bed. Any suggestions?

I've got a few ideas but wanted too see what you folks would do in this situation. Let's stay away from the "build some kind of shelter for the truck" ideas as that just isn't an option for me right now.

thanks