Do i really need a TT with enclosed underbelly?

I've owned TT's both with and without underbelly cover, and find that without, the TT gets much colder at night that the one with underbelly. I was surprised at the difference. I'm using electric space heater, not the ducted propane heater, so whether the underbelly is heated or not is not a factor. So I probably would not buy an RV without underbelly cover in future.

My travel trailer has an enclosed underbelly which is nothing more than corrugated plastic with some foam sealant around the various protrusions, but it also has a heat duct that heats it. I haven't read that section of the manual yet, since I've only had the trailer a week, but I'm guessing that it would protect against light freezes while camping as long as we are comfortable inside the trailer the pipes should be. Of course the water hose coming to the trailer is a different story.

I think it is of more value to just keep pests and road crud away from your underside. I don't think there is too much insulation property there, although some TTs also pump warm air from the furnace into the underbelly, so that could be important if your FW tank is mounted below.

On our Starcraft 235 fb, all the tanks are beneath the floor. Without the coroplast, there are all the wire and fittings for tank monitors, etc exposed to road mud, slush and salt ( in winter). The underbelly keeps all that protected from the elements.

On the other hand, the underbelly keeps you from seeing what is going on, or from identifying any leaks...until the water seeps out of the coroplast. I pulled one end of my underbelly down and found my FW tanks were sagging quite a bit. I ended up taking the coroplast completely off and adding additional support to the tanks, then reinstalling the underbelly. If I hadn't peeked, I might have dropped my Fw tanks along the highway.

I can see the benefit of keeping rodents out, or even late season camping to keep the trailer warmer on chilly nights. I wouldn't call it a necessity however.

My TT has a heated and enclosed underbelly, I slept in it in below freezing temperatures, and the floor still felt ice cold on my feet, and the heat still ran all night.

Our Open Range has a heavy duty "cover" that prevents rodents from getting in, nesting, chewing wires, etc. It also holds heat better and is a great feature when you camp in colder areas. It also protects tanks and other items underneath from anything like rocks and FOD from getting kicked up while traveling.