wooden hull repair

[GibsonGal]

i have an 80x20 foot rectangular houseboat with a flat wooden hull that is seriously rotting. the boat was built in 1929 (it's old). for about 50 of those years it has been in the water year round. the boat sits at a dock in the fall winter and most of the spring, and in the summer it is taken out to a mooring. over the years the wood has been warped from the anchor pulling down one end and batteries at the other ( this was my father's doing- i have fixed that, and the warping has stopped but it is still curved). therefore there is only one expensive way to lift the boat out of the water. so maintainence on the hull is extremely limited.
we have already wrapped the hull in a large sheet of firestone rubber which has done well for 3 years but we recently found at least 5 sufficient rips.

so we need a new hull/ or casing for our existing hull.
here are our limitations/requirements
-we are in brackish water (material cannot deteriorate in any type of water)
-we are limited in travel, we are located just north of the bay bridge in the chesapeake bay in maryland. we need a location on the east coast.
-it needs to last at least 50 years with MINIMAL maintainence
-we cannot pull out of the water more than once in 5 to 10 years.

any ideas on
-choice of material/hull
-company to contact
-location

please help