Grease vs silicone

do whatever your owners manual says to do.

you should "grease" the cables Via the grease fittings underneath the trailer.

Silicone can be used on the 4 uprights.

When we had a popup, I wiped my cables lightly with white grease the first time. I sprayed silicone the next several times thinking I didn't want ever have to deal with getting a bunch of gunk eventually coating everything. Only had the popup for 3 years, so no way to tell if silicone was enough.

At least from a 2004 Rockwood owners manual, I find the following:

1. Clean and recoat lifter posts externally with a rust prohibitive non-drying lubricant.
2. Grease zerks on front bottom and back top of master tube annually.
3. Lubricate springs annually by cranking roof to up position. At each junction of telescoping post lubricate with 90 weight oil into opening between two posts. Wipe off any excess oil on external portion of post to avoid tent damage.

Page 6 has an excellent exploded diagram of the lifting system in the 2004 Rockwood Owners manual.

Unfortunately, it doesn't expressly say anything about the cable, but following the manual, I would indeed use a "rust prohibitive non-drying lubricant" which sounds an awful lot like oil. A silicone grease should work as well, just not the spray that is solvent-based and evaporates to leave a dry lubricant.