I suspected the same thing. The foam was my attempt at covering up the hole until I could address the problem long term. This section is under the sill plate. I have floor pan steel cut into sections ...
just need to get them fitted in. I treated the floor with a rust converter and will put patch material temporarily over that hole until I can get it welded up right.

 

that hole is in fact a cut from factory for access to the mounting bushing that holds the panel that secures the outer sill onto the truck. there is one about 6" in from each
door pillar. I cut two pieces of sheet metal and cosmolined them to put under the carpet for strength. I then treated the floor where the rust was forming and will be patching the holes
for the time being. froggat's in the UK has panel replacement pieces pre-cut for fixing the sill's which I'm hopefully going to source for fixing the edge piece that the
door seal goes on. that I'll definitely have to get tack welded on.

 

I found a donor disco at a junk yard with same color and the floor is in very good condition. lifted the carpet and the paint is still on the pan. good news...
how should I go about removing the pan? is there a method to getting it out so it's usable to put into another rig easily? I presume I have to do it in sections.
anyone done this that can offer some guidance? I plan on bringing a grinding cut off tool, hammer and chisel to perform the surgery.

thoughts are welcomed....

 

Sawsall and/or angle grinder. Cut out more than you think you need. You can always trim it back later but guaranteed you will find more rust than you thought you had.

 

the plan (in my head...) is to cut as close to the sides as I can get the grinder wheel butting up against the seat mounts. On my rig that is where the rust stops. Looks
like the carpets got soaked and were left in that condition for a long period. (before I got the rig). Along the edge of the door post (A pillar) where it meets the floor along
to the mid point of the drivers seat under the sill was rotted. I will be cutting that section out to stitch in. Are there a lot of tack welds holding these panels down or are
the welds mostly on the sides around the perimeter? ie: will I be hacking with the hammer and chisel to free the panel(s) up?

 

I bought a 3" dewalt cut off tool (battery powered) for the job but brought along my old porter cable saw-zall.....the saw-zall was the winner hands down. it chewed thru
the metal like butter. working on the spot welds now. land rover put some black rubberized crap all over the floor covering up the spot welds. what a PITA. I suspect
the tool to remove this coating would be an angle grinder with a stiff bristle cup attachment....but there is no power in the yard...just battery powered devices....

 

question: where does the fuel line run along the floor underneath from the tank to the fuel rail?? want to be 100% sure about this when I cut the floor out of my rig. 2003 Land Rover Discovery 2.

 

You can put dry ice on the rubber and freeze it, then chip it off. might be easier than a wire brush.

 

using a hammer and chisel thus far. waiting on a new drill to see if the aggressive wire wheel cup will be more effective.

 

got the section needed from the donor rig today. drilled out the spot welds and a light tap with a rough chisel and it popped out. now to dismantle mine, remove the seat, amp, carpet and see the full
extent of the rot....

here is the section I cut out: