I used to fish a 10" jon that I got from my late uncle. He wasa welder and fabbed up some mounts for the seats to be attached to the benches. The way the mounts attached was to a lip that extended maybe 1/2 inch to the front and 1/2 inch tio the back of the bench. These mounts were then bolted to the extended lips and it worked VERY well.

This 12 Ft Jon Boat is different ,the benches are wider and there is no lip anywhere on these benches.

I would like to use the fabbed up mounts on the wider benches of this 12 ft Jon but I dont have the foggiest Idea of how to install the mounts. The aluminum on the benches is very thin and I know if I try to take self tapping screws and mount the benches straight to the bench,the screws will pull right out. The Benches on the 12ft Boat are totally virgin. They have no holes and no tampering. I dont want to just go and start trying to install these mounts with a trial and error attitude. I want to do it once and be done.

Any thoughts?

These are the fabbed up mounts im working with

These are the Benches Im working with

This is one of the seat mounts just laying on the bench

Other Mount on the back bench. The pedestal is just for mock up at this point.

If you are wanting to mount those brackets on your seats, I would suggest using rivnuts. If you don't know what they are, look here http://www.cardinalcomponents.com/fasteners/RivnutDesignGuide.pdf The Rivnut® EZ Flat Head Round Body is the one I would probably use. WWW Graingers carries some, they might have what you need. They do require a little practice and a special tool, or some redneck engineering to install, so I would suggest you practice with one or two in something besides your seats first

Look at their C 722 Wrench Type Stroke Tool to install them.

The aluminum seat material appears to be too light to take the strain of supporting the seat on its own.  After time, the nut rivets or nut certs would tear out.

I'd suggest a piece of 3/4 inch plywood that is the dimensions of the seat top.  At each end, use 3/4 inch oak beveled along one edge so that when secured to the plywood will fit accurately to the side of the boat.  The length of the oak should be the same measurement as the width of the seat.

The width of the oak should fill the space between the plywood, and the lip of the rail cap.  It appears the rail cap has a "flange" to which the aluminum side is either riveted or welded.  Screw the oak to the plywood, slide into place, then bolt the assembly through the flange on the rail cap.  The rail cap should be substantial enough to take the strain.

Before you finally bolt the assembly in place, ease all the edges with sandpaper or a router if you have access to one, paint thoroughly and you're good to go.

Fishing Rhino has a good idea with the wood top and seems to be a popular way of doing it when i was searching to do my jon boat..I went with toggle bolts and aluminum plate mounts. They have held 250lb me just fine no movement at all. I can lay back twist and lean foward and the seat it solid! Here is a picture. I think the general idea could work for you.

I have these for my 12 footer. Jon Boat Clamp $28.00 at Bass Pro Shops. Works good.

No way would I bore a big hole. The seats are probably filled with floatation foam and you would also have to dig a large amount of that out. Also, if you decided the mounts didn't work, look what a mess you would have in the middle of your seats.

For how far the load is distributed with the brackets he's mounting, rivnuts should work just fine. That's not one of those cheap Sears, beer can aluminum boats. I've used them many times in similar situations.  I would drill a second hole in each of the ends and put two per end.