I have sprayed Fluid Film on my Jeep Wrangler every Fall. I buy the spray cans on Amazon and spray the frame before winter hits.
By Spring the chassis is coated in salt and grime, and I simply pressure wash it off.
All summer the frame beads water from the leftover Lanolin residue. I repeat with a fresh coat in the Fall again.
I do not have any rust on the frame, even after using it in the PA winters. I only wash the salt crud off in the spring.
I decided to do a test with some similar products out there. I do not use rubber undercoating since this traps the moisture and rust.
I sprayed raw steel with Fluid Film, Protection First Class, Pro Fleet Care ROC40 and bolted it to my front bumper last October.
I drove around all winter with these plates exposed to the salt and elements.
I pressure washed them off twice during the winter.
This is a raw steel plate that was not coated in any rust protection. I only added this in December as a sample data point.
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This is a raw steel plate coated in Fluid Film. Coated in October.
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This is a raw steel plate coated in Protection First Class. Coated in October.
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This is a raw steel plate coated in Pro Fleet Care ROC40. This is the same product used by Pro Fleet Care when they come out and spray your vehicle for you. I only added this in December when I added the other non coated plate for data. It was on 2 months less than the Fluid Film and Protection First Class, and is almost as rusty as the non coated plate.
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So you can see by the results above, Fluid Film and Protection First Class performed very similar. I think Fluid Film is a slightly better product from the results I am seeing, but Protection First Class does come in a larger bottle for slightly less cost. The Pro Fleet Care ROC40 performed very poorly and the coating disappeared rapidly. It was very similar to a thin oil. It dripped off right away, vs the Fluid Film and Protection First Class that was thick and stayed where it was sprayed.
Pro Fleet Care will come spray your vehicle for $160 and apply ROC40. I can spray my vehicle with Fluid Film for $30-60 in material.
My co-worker sprayed his truck with ROC40 and it dripped oil everywhere for a week. The Fluid Film on my Jeep did not drip at all.
The Fluid Film is messy to apply by yourself, but has a big cost savings and better performance.
Both have pros and cons. I have not applied rust prevention to my Model 3 yet, but when I do, I will choose Fluid Film.
*I am not endorsed by any of these manufacturers. I did this test on my own and paid for the products myself.