Replacing Gas Tank Cover with a new one

[Aquaman25]

Hi Guys, sorry I haven't been to active theses days,I'm just getting over pneumonia ,I can't believe I got it in in the summer,anyways,
I can't believe the work you guys do ,some of it is out right ingenious, this why I am asking this question.
I have to replace my gas tank cover,I put a new tank in but I was not able to replace the lid,even though I new it needed it,it was heavy and soaked with
water,I will Finnish this season,tear it apart ,along with other stuff,more later on that.
what is the best material to use? marine plywood is what I was thinking with some sort of bracing,but I am limited because of my new tank,I will
have only 3/4 in below the top layer to play with ,any suggestions would be appreciated .
It needs to be strong because my sons are big guys and so am I.
Thanks in advance  
Jay

[RickK]

If you have 3/4", plenty of room.
If so, follow the examples by members like Slvring on how he stripped the wood from the back of his tank hatch.  Grind the old remaining wood off the bottom of the hatch. You can go back with 1/2 or 5/8" plywood, cut the edges at 45 degrees and coat it real well with resin and let it harden.  Grind the wood down . both sides, enough to knock the shine off it and lay it on a level floor with visquene under and around it. Then mix some resin with cabosil and make it about as thick as peanut butter, use a 1/4" notch trowel to spread it out, set the wood in the putty and put some cinder blocks on top to put the pressure on it.  Make sure the floor you put this on is level or you may find your wood in a different place when it hardens.  After it hardens, lay some mat or cloth on the exposed wood and down the 45 degree angles into the bottom of the hatch. let it harden and you're done.  Another option is to use some 1/2" plascore composite and lay some cloth on both sides and then stick it to the bottom of the hatch as described above.  Much lighter and as strong or stronger that the wood.

[wingtime]

I was able to peel apart my old tank lid.  The wood came right out leaving me what looked like a giant shoe box lid.  I laminated in a new plywood core and glassed in the bottom.  Easy as pie.

[Aquaman25]

Thanks for the ideas guys,but I want to build a new cover and not use any of the old,I went from 120 gallon aluminum tank to and 80 gallon
plastic tank, and none of the holes match the new sending unit or pickup tube,poor planing on my part but I new I was going to
replace the cover anyways,the rest of the wood on the boat is solid,the guy before me and the age just did the cover in.
I would like to use 3/4 Marine ply with a couple of layers of bilateral layup,underneath I would like to put 3/4 in cross sections of
8" wide support sections spacing them x amount of inches apart,gluing them in place and then covering them with a thinner layer of glass.
I will not be putting the original seating back in,because the chair on the port side makes it very difficult to get into the cabin.
I am going to have a custom leaning post made for the drivers side that will allow the back to swing forward so i can sit facing the stern.
If you guys have any links I can get ideas from please post them,I would be most grateful,it's very hard for me to sit here right now and type,
so let me know what you think of my idea and thanks again for the advice.
Jay

[fishinonthebrain]

I am going with 1/2" coosa in my lid. Never have a problem again with it and will lighten it up a bit too. Just a suggestion.