Building a Javron super cub and questioning whether to cover the bottom to the tail end or leave it open above the tail wheel like some do? Thoughts or suggestions?
Plus and minus. CO influx is real when open, and so is snow buildup when parked in a storm. Closed it's sealed but inconvenient to inspect for snow and crud that can get in through the trim covers (or ?) unless they're temporarily plugged with foam. On one plane I had a clear inspection cover so I could look at that area. Made it from poly plastic riveted to inspection cover clips.
Like Mike says also for another consideration, when the entire section is covered as Piper did it dirt and moisture will collect between the bottom longerons in the triangle ahead of the tailpost. This will cause the longerons to rust out $$$$$$$. Leaving the fabric off, the dirt will not become trapped.
Why not the Attlee Dodge "metal belly pan". I have one installed on my Cub. It has four quick disconnect fasteners and runs about 24 inches or so from the tail forward. Easy install. My mechanic suggested it to me and it takes all but five minutes to take off and put back on after the annual inspection. You would not believe the crap that this protects the longerons and especially the stabilizer jack screw from debris, especially in Alaska. It is not completely airtight and lets the slipstream kind of blow out any moisture that would be trapped there. You just drop it down anytime to see if there is any corrosion or debris trapped in this critical area of the fuselage. Since I have had this on for over 20 years I have had no problems. It also does not rattle and make noise like the full "metal belly pans". I would not be without one. Not expensive at all. Need a mechanic to weld the fastener gussets on the longerons for the fasteners to grip. They come with the package, instructions and STC. not expensive at all.
The key area which collects the wet dirt is the triangle starting at the tail post going forward above the tail spring. Your belly pan starts ahead of the tail spring. Make sure that this triangle is open on the bottom.
Also the side triangles above the bottom one being open help keep the bottom clear and assists with visual inspection.