Does The RV Fuel Vault cover both diesel and DEF on my DX3?

Yes. It covers and secures both the diesel fuel cap and the DEF cap in one armored enclosure.

Will it fit every DX3 floorplan?

Yes. Every Dynamax DX3 shares the same Ford F-550 chassis and filler configuration. Fits all floorplans.

How is this different from a locking fuel cap?

A locking cap protects one filler and can be pried off. The RV Fuel Vault is a full armored enclosure that covers and locks both diesel and DEF caps simultaneously.

How long does installation take?

8-15 minutes with basic hand tools. No drilling, no cutting.

Limited Lifetime Warranty plus a 30-day satisfaction guarantee.

Built for the DX3

Dynamax DX3 Locking Fuel Door — Armor for Your Super C

The Dynamax DX3 is a luxury Super C built on the Ford F-550 with the 6.7L Power Stroke diesel. Despite its premium price tag, Dynamax left the diesel and DEF caps completely exposed. The RV Fuel Vault is the exact-fit armored locking enclosure your DX3 is missing.

The RV Fuel Vault — Dynamax DX3 — locking fuel door for motorhomes

The Problem

✖Your Dynamax DX3 has exposed, unlocked diesel and DEF caps — no factory fuel door
✖The F-550 Power Stroke carries 50-80 gallons of diesel — easy pickings for thieves
✖DEF contamination can destroy your SCR system — $5,000-$10,000+ to repair on a luxury Super C
✖Generic locking caps do nothing for your DEF tank and can be defeated in seconds
✖Road grit and diesel splash-back slowly damage the finish around your exposed filler necks

The RV Fuel Vault Solution

Factory-finished look — eliminates exposed caps on your DX3
Precision-engineered for the Ford F-550 filler neck configuration used in your DX3
Tamper-resistant keyed lock secures both diesel fuel and DEF fluid
High-strength fiber-filled polymer — complements your DX3's premium build quality
Bolt-on in 8-15 minutes — no drilling, no cutting, no modifications
Corrosion-proof — rated for full-time use in any climate

See the Difference

✖ Exposed caps on DX3 — no security

✓ RV Fuel Vault installed — sealed and locked

Why You Need a Locking Fuel Door

Lead with finish. End with security.

Factory-Finished Look

Eliminates the exposed plastic caps on your DX3. Your luxury Super C finally looks complete.

Fuel Theft Prevention

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

DEF Contamination Defense

Prevents tampering with your DEF tank — avoids $5K-$10K SCR system repairs.

Vandalism Protection

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

Installs in 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 Ford F-550 (Dynamax DX3) Motorhomes

The Dynamax DX3 is built on the Ford F-550 with the 6.7L Power Stroke diesel. Both diesel and DEF filler necks are completely exposed from the factory.

Manufacturer	Models / Floorplans
Dynamax DX3	All floorplans (37TS, 37RB, 34KD, etc.) on Ford F-550
Dynamax Force HD	All floorplans on Ford F-550
Also fits other F-550 Super C	Entegra Accolade XT, Jayco Seneca

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

Frequently Asked Questions

Common questions about The RV Fuel Vault on Ford F-550 (Dynamax DX3) motorhomes

Not Sure If It Fits Your Rig?

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

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Order Today — Starting at $99.95

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

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Proudly Made in the USA · Patent Pending 64/085,223 · Est. delivery by July 4, 2026