What is a DEF cap cover for an RV?

A DEF cap cover for an RV is a locking enclosure that protects your diesel motorhome DEF (blue) cap from tampering and contamination. The RV Fuel Vault locks over both your DEF and diesel fuel caps to help prevent costly SCR-system damage.

Why is DEF contamination such a big deal?

DEF must be pure urea solution. If contaminated, it can destroy the SCR catalyst and sensors. Repairs cost $5,000-$10,000+ and may require towing.

Does The RV Fuel Vault cover DEF only, or fuel too?

It covers BOTH your diesel fuel cap and your DEF cap. Dual protection with a single install.

Is DEF tampering really common?

DEF caps are easy to spot (blue) and easy to open. Incidents are on the rise as diesel motorhomes become more popular.

Does it fit my diesel RV?

Ford F-550, F-600, and Ram 5500 Super C chassis. Use our Fitment Finder.

Limited Lifetime Warranty plus a 30-day satisfaction guarantee.

The Part the Factory Forgot

DEF Cap Cover for RV — Protect Your Diesel Exhaust Fluid

DEF contamination can destroy your emissions system. The RV Fuel Vault covers and locks your DEF cap alongside your diesel cap — preventing the $5,000-$10,000 repair nobody wants.

Order Now — From $139.95

Patent Pending Made in USA Free Shipping Ships July 2026

The RV Fuel Vault — Locking Fuel-Door Enclosure — locking fuel door for motorhomes

Why a Locking Gas Cap Is Not Enough

✖DEF caps on Super C motorhomes are completely exposed and unlocked
✖Wrong fluid in your DEF tank can destroy the SCR system — $5,000-$10,000+ repair
✖DEF contamination may not be covered by your warranty
✖Exposed blue DEF caps are easy to identify and tamper with
✖There is no factory DEF cap cover or lock available for motorhomes

Why a Locking Fuel Door Beats a Locking Gas Cap

Covers and locks your DEF cap alongside your diesel fuel cap
Prevents DEF contamination — the most expensive tampering risk on a diesel RV
Tamper-resistant keyed lock stops both fuel theft and DEF sabotage
Factory-finished look for both filler neck areas
Bolt-on in 8-15 minutes — no drilling, no cutting
Fits Ford F-550, F-600, and Ram 5500 diesel Super C chassis

Before & After: Your RV's Exposed Fuel Cap vs. a Locking Fuel Door

✖ Exposed cap — no security

✓ RV Fuel Vault installed

Why You Need a Locking Fuel Door

Lead with finish. End with security.

Factory-Finished Look

Eliminates the exposed plastic cap. Your rig finally looks production complete.

Fuel Theft Prevention

Keyed lock stops siphoning at campgrounds, rest stops, and storage facilities.

Contamination Defense

Prevents sugar, water, or foreign substances from being added to your fuel tank.

Vandalism Protection

Tamper-resistant design deters opportunistic damage to your fuel system.

How It Installs — 8–15 Minutes, No Drilling, No Cutting

8–15 Minutes

Average install time

Basic Hand Tools

No special equipment needed

100% Reversible

No drilling, no cutting, no mods

Compatible RV Models — Which Locking Fuel Door Fits Your Motorhome?

The RV Fuel Vault DEF cap cover fits all Super C diesel chassis with exposed DEF filler necks.

Manufacturer	Models / Floorplans
Ford F-550	Thor Magnitude/Omni, Dynamax Force/DX3, Entegra Accolade, Jayco Seneca
Ford F-600	Thor Magnitude/Omni Super C, Entegra Accolade XL
Ram 5500	Dynamax Isata 5, Grand Design Lineage

Don't see your model? Use the Fitment Finder — we likely fit your rig.

Frequently Asked Questions

Common questions about The RV Fuel Vault

Not Sure If It Fits Your Rig?

Our Fitment Finder checks your exact year, make, model, and floorplan in seconds.

Find My Fit

Order Today — Starting at $139.95

Single Door, Set of 2, or 3-Pack · Free Shipping · Limited Lifetime Warranty · 30-Day Guarantee

Order My RV Fuel Vault

Proudly Made in the USA · Patent Pending · Est. delivery by July 31, 2026