hi, all. here's some more food for thought. while waiting for my valves to arrive i decided to look at some other things. the car always smells musty and last summer it got invaded by ants. there were thousands of them which i mitigated with borax. the ants are gone now but the musty smell remains. i looked everywhere and couldn't find their food but finally pulled out the rear seat bench. there are two wells there and apparently something got spilled in there. the foam is ruined and the seat wire frame is terribly rusted. i think someone spilled some soda or something into the hole where the seat belt buckles are! no wonder it got invaded by ants! ...anyway i am thinking about just cutting a board to fit in there. i see some old posts about it but no one is offering a template. has anyone tried this? what's a good way to draw the curve in the side panels? wire? what to put underneath to block noise? rockwool?

 

First of all, for the musty moldy smell might also be coming from your HVAC system, remove and replace your Cabin Air Filter ( ) as for the rear seat delete, I would use CAD (Cardboard Aided Design) make your template out of cardboard first then cut some plywood to fit, cover it with some suitable fabric of your liking to cover it. As for sound deadening I would recommend so sort of self-adhesive cavity filling but not loose, many to choose from but should be taken into consideration when working with CAD so you can ensure proper fitment. Or.. you could just get this ...
at ECS Tuning
2006 MINI Cooper John Cooper Works GP Coupe L4 1.6L Interior Seats Rear Seat Delete - 1928314 - MINI Hard Top Rear Seat Delete Panel R50/R53/R56
... or at Turner Motorsport
1928314 - MINI Hard Top Rear Seat Delete Panel R50/R53/R56 | Turner Motorsport
Either way,

Motor On!

 

yeah that's something i can get if i get it running again with no codes but i dont think it's the cabin filter. it smells when you just get in after it sitting and the smell goes away when driving it even when using the filter. the seat bottom is nasty and it smells plus the rust from the cage is impregnated into the foam. i can just imagine the kids snickering and pouring their juice into there
haha cad. maybe i can stuff an old memory foam pillow in there

 

I haven't done it on a Mini but back in the day of my classic VWs; I simply used the backseat as a template tracing the outline on top of a piece of plywood. A bit of trimming/refining the contours hear and there made for a perfect fit. Especially after covering in auto grade carpet.

'might work for you. Might not - just a thought from my experience.
BTW: When I pulled the back seat of my Mini (a couple of years ago) to change my fuel filter, I too discovered some sort water egress under the seat area. The under cushion had been saturated. I traced the source of the water/moisture to the upper roofline trim/drip rail, which had a dry rotted tear in the rubber allowing rain water to make its way down behind the interior side panels/down to the seat cavity.

 

on further inspection i think i have a similar issue. there is rust on some of the rear seat torx connectors higher up and i recall now years ago i had leakage. at the time i thought it was from a broken upper brake light cover, which i replaced. i remember the original jack kit the the back got all rusted. i replaced that cover and didnt see any more leakage but maybe it found it's way down there. doesnt explain what attracted the ants though

 

Regarding the ant infestation;
Yup - I also recall having my Mini invaded by ants at one time.
I lived in Florida and during the late Spring through late Summer can experience some torrential down pours.
If I recall correctly; In mid-summer of 2006 or '08, I rained constantly nonstop for more than a week straight. The ants sought higher ground - into my Mini. Into the interior as well as under the hood! I remember killing them off with a natural ant killer spray. I had ant bait/traps tucked into a few corners inside the cabin and engine compartment for a couple of years then and afterwards.
Of course, I'm not suggesting that is/was your case.
It just reminded me that it also happened to me almost 20 years ago.