This is the most complicated part of the construction and is the most troublesome area that everyone talks about. There is about as many hatch designs as there are Teardrops. You can have a choice of wood or steel framework with plywood covering it. We were concerned with the hatch because of the rough terrain it would be subject too. Many Teardrop hatches leak at their gaskets and at the piano hinge. Most have solved the piano hinge leaking problem by using a strip of vinyl under the hinge. We chose to use a special one called a truck canopy hinge, which is available from Grant Whipp of Tales and Trails. It comes in 60" lengths and has a very unique design. Another concern of ours was making our kitchen dust proof. While driving down dirt roads and the Teardrop trailing behind, I doubt that we'll actually see it in the rear view mirror. So we had to keep all these considerations in mind while designing our hatch, dust and water proof, strong but light weight, insulated from the desert sun and supported to withstand unpredictable winds. You'll need to know what type of molding you are going to use ahead of time before you design your hatch too.
Profile We first traced the hatch area when the body was first constructed. This profile ended up not being accurate after installing the "L" molding on the kitchen walls, which slightly changed the radius. Plus you have to consider the thickness of the weather-stripping, which will change the radius too. We purchased this molding from McMaster-Carr Industrial Supply and applied silicone under it and used #4x1" stainless oval head screws. The internal width of the molding is the required 13/16" which was the total thickness of the plywood and 2 layers of Filon siding. Your larger True Value hardware stores have a large variety of aluminum moldings to choose from.
Ribs We traced the kitchen walls onto a 1/4" piece of plywood adding 3/8" to the radius. We cut out this template to start making the 6 internal hatch ribs. The truck canopy hinge is 2 pieces of extruded aluminum angles that are hinged together. Keeping in mind that 3/8" of an inch clearance was needed between the roof and hatch, we cut 6 ribs out of 3/4" plywood and made the ribs 1 1/2" thick. Some of the ribs had voids in the plywood so more had to be cut.
Cross braces 2 pieces of Red Oak 3/4" x 1 1/2" boards was glued together at the top frame of the hatch where the hinge attaches. 2 pieces of Poplar 3/4" x 3 1/2" boards was glued together at the bottom which will support the draw type hood latches and base for the recessed tail lights and license plate. Poplar 3/4" x 1 1/2" boards were used for the cross braces. Additional boards were installed to the outside ribs to support the gas charged lift support shocks which will be used instead of support rods to hold the hatch in the up position and keep it secure in the wind.
Assembly We found out that it was easiest to assembly all the pieces while on the back of the trailer with the hinge in place. Since the hinge is actually 2 pieces of angle jointed together, this helped lock the hatch frame into place while assembling it. Using wood shim spacers, we clamped the 2 end vertical ribs to the sides leaving a 3/8" gap between the sides and hatch. Then we took the measurements for the horizontal top and bottom cross braces and attached them using screws, 'Heavy-duty Construction' Liquid Nails and Stanley metal corner angle brackets. 3/4" x 1 1/2" Poplar boards were then used inside the remainder of the hatch so we'll have something solid to nail the 1/4" Lauan plywood skin into while the adhesive is drying. We tried the 'Sub floor' Liquid Nails but it was too runny and took too long to dry. Again, we found out that nailing into the end grain of plywood will not hold the plywood in place while the adhesive was drying. 1/4" Lauan plywood is actually 3/16" in thickness and we felt that this Benroy hatch radius was just about it's limit for bending. The plywood was measured and cut over sized so it could be trimmed to fit later. The hatch was clamped and braced into position on the back of the Teardrop while all the adhesives where drying and keeping it from springing back. Did it spring back? Yes and at this point I had to throw the first hatch away and make a second using a 1" tighter radius to compensate for the spring back.
Hatch Siding We applied the Filon to the sides while it was 60 degrees with no problems. The roof Filon was applied during 50 degree weather with 100% humidity and there was complications with the Stabond adhering. We applied the Filon to the hatch in 104 degree temperature and the Stabond worked great. We attached Filon under the over lapping hatch edge and sides, covering all exposed wood. Using a laminate blade in our jig saw designed for cutting Formica, we cut out the openings for the recessed tail lights. This special blade has it's teeth reversed in the down direction in order to make a clean cut through the laminate and it worked well.
Wiring and Insulation Using 16 gauge wire for the tail, license plate and inside hatch lights, the connections were soldered together and heat shrink insulation was applied. A plastic 1 1/2" x 2" x 4" electrical junction box was used to terminate the wire connections and where a jumper cable will be attached between the hatch and body. The voids in the hatch was filled with 1 1/2" polystyrene foam. We added a wooden backer block for the kitchen light. Remember where the wiring is so you don't nail through it.
Interior hatch was covered using 1/8" Lauan plywood and covered with Filon. After all the work and expense in building the hatch, I couldn't see myself attaching one of those $10 porch lights so we'll be installing a $30 Thin-Lite brand light with a 18w bulb and amber lens to keep the bugs away. This light works great and you can read by it and yet it's easy on the eyes. The seam edges was sealed using white GE's Windows and Doors Silicone II and 1/4" x 1/2" aluminum angle purchased from Mc Master-Carr. This grade of silicone is much better than the standard and costs a few dollars more. Not all silicones are created equal. This silicone has a longer drying time and sets up harder and doesn't peal off as easily as standard silicone.
Hatch molding is a 1 1/4"W x 13/16"H Wide Lip Insert molding purchased from All-Rite for $36.00 per 16' length. This helped match the contour of the rest of the bodies 1 1/4"W x 5/8"H Corner Insert molding, purchased from All-Rite for $32.00 per 16' length. The 16' cardboard shipping tube which held all this molding cost $50.00 freight by common carrier due to it's size. UPS only ships up to 8' lengths. We fastened the hatch molding using 3/16" large head pop rivets and the ends were sealed with silicone. The bodies corner molding was fastened using #8 x 3/4" PPH stainless screws. Black rubber insert strips will be added later to cover the fasteners. 1/8" x 1" aluminum strap from Home Depot was used around the bottom of the chassis. After installing all the molding & hinge, we removed all of them, cleaned everything with acetone, applied silicone and reattached them. Insert molding has been known to leak because it puddles the water so make sure you do this procedure.