[Wavery]

One option for a black tank is to make your own out of thin plywood skin (19.5"x19.5"x9") and fiberglass it on the inside and out. It's a lot of work. I did mine in place and used the floor (covered with layers of fiberglass) as the tank bottom.

My recommendation would be to build a complete box outside the trailer. Fit the box in place and make sure that it fits lightly snug. Install the drain pipe in the box. Do all of the fiberglassing (inside and out) in an open area. Glass the bottom and sides (inside with 4 layers, outside with 1 layer) first. Then glass the top (made of 1/2" marine plywood) as a separate unit. While the glass is still tacky, lay the top on the box and glass the edges. Allow the assembly to set, then install it.

Because of the toilet that I bought, I had to make the top as a separate panel. I had to install the toilet the the new tank top, then I laid that assembly down last with sealer and screws. The reason that I did that is because it would have been impossible to attach the new toilet to the top with the top in place. (poorly designed Thetford toilet). I recommend buying a toilet that mounts with external screws (like your home toilets) and nuts.

This option takes some careful measuring and experience with fiberglass. I made a 13.5G tank that sits on the floor, under the toilet (much like the Sealand). I've had it out on 3-campouts so far and it works great. It perfect for 5-days with 2-people.

If you are interested in doing this, I can give you more complete instructions. This is just a brief over-view of the procedure.