What is DEF and why do thieves target it?

Diesel Exhaust Fluid (DEF) is required by all modern diesel engines for emissions compliance. DEF theft and contamination can disable your motorhome and cost thousands in repairs.

Does The RV Fuel Vault cover the DEF cap?

Yes. The 3-Pack option at $459.95 includes a dedicated DEF cap cover with the same tamper-resistant locking protection as the diesel fuel covers.

What happens if someone puts the wrong fluid in the DEF tank?

Contaminating a DEF tank with diesel, water, or other substances can destroy the SCR catalyst and related components, potentially costing $5,000 to $15,000 in repairs.

Which chassis have DEF caps that need protection?

All modern diesel motorhome chassis have DEF systems, including Ford F-550/F-600 Super C models.

Locking DEF Cap Cover for RVs | DEF Theft Prevention

The Problem

✖DEF can be siphoned or contaminated in seconds — the exposed blue cap is on the same side of the chassis as the fuel cap

✖A single improper fill (water, sugar, diesel, windshield washer) destroys the SCR catalyst and exhaust sensors — $8,000–$20,000+ to repair

✖Insurance rarely covers emissions damage from tampering — the owner pays out of pocket

✖With the engine in regen or limp-mode, a contaminated DEF tank will strand a $400k motorhome in the middle of a trip

✖The blue DEF cap is an ugly, exposed eyesore on otherwise finished Super C, Class C, and Class A chassis

The Solution

The RV Fuel Vault 3-Pack includes an armored DEF tank cover — same patent-pending keyed lock as the diesel fuel doors

Armored 3/16″ High Impact Reinforced Material physically seals the DEF fill neck — nothing goes in or out without the key

Tamper-resistant keyed lock — same key opens diesel and DEF doors for fast fills

Eliminates cross-fill risk at busy truck stops — no more sleep-deprived mistakes with the wrong cap

Bolt-on install with no modifications to your motorhome chassis

3-Pack with DEF cover: $459.95 (MSRP $569.95). In stock — ships within 3 business days. Limited Lifetime Warranty. Made in Sarasota, Florida.

RV DEF Cap Cover: DEF Theft and Contamination Prevention

A DEF cap cover for your RV keeps the blue diesel exhaust fluid cap locked behind a keyed door. Diesel Exhaust Fluid (DEF) theft and contamination are growing concerns for motorhome owners. The blue DEF cap on most Super C and diesel Class C motorhomes is completely exposed and unprotected. The RV Fuel Vault 3-Pack includes a purpose-built DEF cap cover with tamper-resistant keyed lock technology.

Locking DEF Cap Cover for Your RV

The Problem

The Solution

Frequently Asked Questions

RV DEF Cap Cover: DEF Theft and Contamination Prevention

Order Today — Starting at $159.95