Should Your Next RV Have an Enclosed Underbelly?

What is the purpose of an enclosed RV underbelly? Does it provide any insulation? If so how much? Is it a standard feature or an upgrade? These are good questions and we will talk about the pros and cons of an enclosed underbelly and if you should consider this feature in your next RV.

If you have no intentions of using your RV in freezing weather, an enclosed RV underbelly may not be necessary, especially if you have to pay extra for it. Some RV manufacturers offer this as a standard feature, while others list it as an option. In either case let’s take a look at what you should look for and questions you can ask your salesperson regarding an enclosed RV underbelly.

The Pros of an Enclosed RV Underbelly

Two trailers camping in the snow.

The main purpose of an enclosed underbelly is to protect waterlines and holding tanks from freezing when installed with insulation. It also provides added protection while traveling from kicked up rocks and keeps road grime and dirt from attaching itself to the under carriage and holding tanks. Another advantage is it does provide better airflow which may improve gas mileage. Cosmetics are yet another advantage along with keeping mice and other rodents from making their home in your RV.

A quality underbelly design will usually include a shield or belly pan made of fiberglass, aluminum or corrugated plastic panels. The best type of insulation that won’t retain water or become loose and fall away from frame and thus lower the R value is sprayed insulation or synthetic foam sheets. The picture above shows fiberglass panels being used as underbelly shield. It does present a nice clean appearance and you don’t have to be an engineer to imagine air slipping smoothly over the surface compared to the tangle of girders normally encountered by a 65 mph headwind during highway transit.

The Cons of an Enclosed RV Underbelly

A poorly designed or installed underbelly cover may let moisture in during extreme conditions
(driving during a rainstorm, for instance) and cause rust by trapping moisture against the frame. This
is a big concern and a number of RV owners have experienced this problem. If fiberglass batts are being
used for insulation they can absorb and hold water if exposed to excessive moisture, increasing the
chance of rust. Fiberglass can then become loose and pull away from frame, lowering your R values and
proving ineffective in preventing waterlines from freezing. Sodden fiberglass batts are also heavy and
a breeding ground for mold and odor –an odor that will drift upward, possibly presenting a musty interior
that no amount of airing out will eradicate.

If the underbelly shield is made of fabric, it could eventually tear and become a problem. We propose
avoiding fabric as the underbelly shield if you anticipate high-mileage or extended trips. It really is fine for light-duty service –and it breathes.

Another potential problem with an enclosed underbelly is lack of access and visual inspection. If you need access to the undercarriage for whatever reason it can be problematic. You may need to remove panels, fabric and insulation to have adequate access. This is both time consuming and frustrating. Also, much like a roof leak, an enclosed undercarriage usually won’t present a minor issue to your attention until it has progressed to a significant problem.

The Verdict

Enclosed underbellies have improved in recent years as manufacturers have learned from past designs. Materials used and mounting procedures have advanced. While an inability to do a quick visual check is still an annoyance, we feel the pros definitely outweigh the cons. That’s especially if you are in the market for a three- or four-season RV that may see freezing temperatures. Some manufacturers include access panels, enabling visual inspections of important electrical and plumbing junctions without the need to disassemble the entire underbelly. This is the best scenario of all options, but generally features only on high-end premium units.