Hmm. I thought you were joking.
Think about this. CLP is a solvent that cleans adequately, lubes adequately and protects adequately. Notice I used the word adequately and not well. You are making a trade off. Convenience in exchange for superior performance. That being the case it is a waste of money to buy a gallon of CLP and apply it on something that is going to sit outdoors in the elements. Even the minimum protection it would afford will be gone inside a month or more likely within a week.
Also it is my opinion that the expiration date on these solvents is largely a tactic to get you to buy more product. As Anni said, it still works, just allegedly not as well. Which was never as well as a dedicated cleaner or a dedicated lube in the first place. I have and use CLP that is older than that, but by and large I buy CLP in aerosol cans so it is never "Open" in the first place.
Far be it from me to tell anyone how to spend their money brother, but as I see it the only benefit in your case to buying a gallon of CLP is the experience of justifying buying a gallon of CLP. Which isn't actually a benefit at all. Do yourself a favor and buy a large size aerosol can of your favorite CLP for $13 and use the money you saved to buy more ammo.
If you want to actually protect your steel solar array I am going to tell you the best way to do it. It's fairly simple, fairly inexpensive and more effective than anything you can imagine.
Step one: Buy a 17 lb Magnesium anode. Bury it 1' deep alongside of your solar array and cad weld the wire to the leg. This will cathodically protect the steel for many, many years. I have one lb. anodes protecting my chain link fence right now and it is something we use to cathodically protect buried steel gas lines. And it's cheap ( free for me). Here is a link to an anode.
Welcome to buy high quality High potential Magnesium Anode from us. Enjoying the advantages of extremely high electrochemical performance, large capacity and lasting service time, this anode products must be your best choice. We can bring you satisfactory service and timely delivery.If you don't...
www.howahanode.com
Here is a link to where to buy this anode.
MG-17LB - ANODE BAG 17LB W/10FT 12TW WIRE H-1 GRADE A;
www.tarantin.com
Step two: Prime and paint your steel with high quality outdoor paint.
Step three: Don't worry about it ever again.