Covered vs Uncovered Underbelly

Enclosed underbellies are a really great way for manufacturers to hide their substandard workmanship and materials... :R

A heated underbelly is very inefficient and a lot of heat ends up in the outdoors. What a waste. Some return air comes back up from the cold underbelly space. I sealed up all the holes that were hacked through the floor for ducts & piping and it made a BIG difference. But we have 100% electric heating now and none goes into the underbelly space. Furnace is rarely used now.

Not being able to access things in the underbelly space is a big negative. Can't inspect anything that the factory did wrong or poorly. Can't fix or replace holding tank valves. Can't inspect for frame damage, wiring or plumbing issues, rodent damage, etc. Can't do wiring or plumbing mods. If a tank or piping leaks and soaks the insulation, it's a real mess and a huge job to fix. Want to install a set of Horst Miracle probes or Seelevel sensors? Fuggedaboutit. I can't see aerodynamic improvement being of any significance amount, if any.

They use batt insulation in the underbelly space which IMO is a bad choice plus they don't do a very good job of installing it. If I had an open underbelly and wanted to camp in cold/colder weather, I'd much rather install insulation myself and do it properly. Heating pads under the tanks would work well. I'd beef up insulation immediately below the floor to improve R-value partly because a cold floor in cold weather is not comfortable, esp. on the feet.

Our first TT had an open underbelly and it was nice to be able to see and access everything under the frame. Had a couple of wiring issues that got fixed under warranty. Enclosed underbellies are common nowadays and you won't always have a choice in having one or not unless you remove it all. The only real plus I can think of would be if you are off-roading in mud. :)

But since in Texas and it's not below 40F or so often, if you find an open underbelly in a brand and floor plan you like, get it. Add rigid insulation afterwards if you think it would help.

Enclosed underbellies do have their pluses and minuses for sure and these have been mentioned in this thread. An enclosed underbelly does improve the aerodynamics but the question here is will that improvement really do much to help your wallet. Those who are quick to dismiss all things as "hype" need to rethink things.

I tow an Airstream and have right at 40K miles on it. The aerodynamics on this thing really do make a difference. After a couple of years we installed a bike rack on the back and I noticed just about a 1 mpg loss in efficiency. It didn't seem to matter if there were bikes attached or not. I used the onboard computer to check and then went to paper and pencil methods and I was down just about one mpg. The rack on the back changed the aerodynamics enough to see the difference at the pump. My underbelly is covered. If I uncovered it I am sure the added turbulence would have an effect.

The issue here is, does the extra turbulence really make that much of a difference to you and is it really all that large? A salesman will push the covered version and make it sound much better than it really is. I suppose this is the hype mentioned earlier. Yes, it is better but how much better? I say, not that much. I like my bike rack and would not think of removing it just to get a bit better towing mileage. This is the same argument I would apply to the underbelly decision. What are the benefits?

since we do a fair amount of cool and cold weather camping, the covered underbelly is a necessity. Even though basically un insulated, it does help keep things from freezing and to keep the underbelly above freezing I just drilled some 1/2" diameter holes in the side of the floor vents to duct some warm air to the underbelly. also helps keep the floor warmer which is a side benefit.

And in very hot weather the covering does help some from heat gain, especially if your parked on concrete or asphalt.

as many has mentioned, I've had both. The covered was a 2000 Trail Lite. It was very aerodynamic and I do think the smooth under belly helped. Didn't like it cause would have to cut the material to fix stuff. My current TT, a '05 Trail Cruiser doesn't have enclosed underside but us very smooth under there, just a waterproof membrane glued to the laminated panels the whole trailer is made of. The grey and black tanks are wide and shallow so don't hang down much, and it has the Dexter torsion suspension so there are just two skinny "axles" going across. I have to disagree with the poster that said smooth under bellies won't help aerodynamics, this definitely does. It's part of the whole Trail Cruiser design that gives it a very aerodynamic shape and even though it weighs more than my old Tahoe, it tows much easier, as wind pressure is more of a negative than weight. A bunch of stuff hanging down on the under side creates a turbulence that prevents the trailer from easily separating from the air stream. Notice a lot of semi's have long plastic panels underneath beginning close together at the front of the trailer and widening out to just in front of the back wheels. This prevents the wind from flowing under the trailer where it would create turbulence.

GrandpaKip wrote:
Having had both, I prefer uncovered. We don’t camp in cold weather, so heat and insulation don’t matter.

Our previous 2007 RVision TrailCruiser C21RBH had a sandwich floor & enclosed underbelly, our previous 2008 K-Z Spree 240BH-LX had a solid wood floor & enclosed underbelly, our current 2014 Coachmen Freedom Express 192RBS has a solid wood floor & open underbelly and I've not noticed any significant difference in comfort level inside any of these camper when the temps are between freezing and ~ 100F. What I don't care for is having to open up an enclosed underbelly for any repairs or modifications I may want to make - a real PITA compared to an open underbelly where the entire underside of the trailer is readily accessible.

Having had both, I prefer uncovered. We don’t camp in cold weather, so heat and insulation don’t matter. I like being able to get to everything easily and I could inspect the tanks and such.
If I could raise it 6’, I’d remove the coroplast and neaten it up. I would think the protection provided by the coroplast is minimal at best. I never had any undercarriage damage on the previous camper.

I'm a fan of underbellies, just noting that the holes in the upper plywood floors are pretty large and appear to be cut in haste. And yes, all of the penetrations in the plastic underbelly should be closed with foam to keep out rodents and dirt/debris.

I have had both.
If you are going to be camping in cold weather it is much better to have it covered and fully insulated.
I personally like it uncovered so I can run any new wires or pipes that I might want to.

Jack L

LAJMINNIEPLUS wrote:
Also with the covered underbelly, the manufacturers take less time in cutting penetrations through the floor because the underbelly will cover the large holes. Without the underbelly, holes for pipes are the size of the pipes. With an underbelly, holes are cut much larger than the pipes and are great areas for mice to travel at ease up from the underbelly. It looks like most holes are cut randomly with saber saws and are just about any shape imaginable. Also, no need to clean up any sawdust or debris because it will all be out of sight.

My Passport has an covered underbelly and the company has all but one opening (that I've been able to access) filled with black (rodent proof?) foam. That single opening serves as a cold air return for the warm air the furnace pumps into the underbelly. That opening is near the hot water heater under the bunk beds were it can get some heat from the tank as the cool air re-enters the cabin.

Besides keeping the tanks and water lines from freezing up and providing a warmer space for the heating ducts, the covered underbelly also helps keep the main cabin floor warmer. We've spent several comfortable weeks camping in places that had nighttime temps in the mid 20's and daytime temps in the low 30's.

IMHO, if you're planning to camp in the mountains or the northern state during spring or fall seasons then a covered underbelly is worth the extra expense.

Also with the covered underbelly, the manufacturers take less time in cutting penetrations through the floor because the underbelly will cover the large holes. Without the underbelly, holes for pipes are the size of the pipes. With an underbelly, holes are cut much larger than the pipes and are great areas for mice to travel at ease up from the underbelly. It looks like most holes are cut randomly with saber saws and are just about any shape imaginable. Also, no need to clean up any sawdust or debris because it will all be out of sight.