A PO butchered a big hole in each kick panel in order to install speakers. Now I want to cover them up with some sheet metal. When I peer into the body cavity (horrible reference) with a light and mirror, it appears that the cavity is totally boxed and is NOT a path for cowl drainage.

The stiffening channels that are pressed into the panel structure make a total seal a bit more challenging and time consuming. If someone knowledgeable about the 1800 structure can confirm my assumption then I will still cover the hole with sheet metal but I won't be so concerned about having an absolute water/air tight seal.

Chris;

Back of that bulkhead is accessible from wheelwell after inner fender (and wheel) are removed...and there should be a drainage provision, although it is typically blocked with debris...

You could install a speaker since the hole is already there...install a foam "cup" sized for the speaker as a barrier between the wheelwell volume and speaker cone.

Cheers

"....You could install a speaker since the hole is already there...install a foam "cup" sized for the speaker..."

I'm toying with the idea of cutting the hole out to 6" square but with slightly radiused corners and installing something like this to act as a "speaker well":

https://www.bedbathandbeyond.com/store/product/duff-square-aluminum-cake-pan/3267306

There's plenty of lip on it so I could use the black foam material as a seal and make it double thick where the stiffening channels are. I checked out some basic speakers online and there are some that are a bit less that 2" deep so the magnets wouldn't hit the back of the pan.

It's much easier for me to clean up the hole to a square shape rather than round.

Ugh - this wasn't supposed to turn into such a high-tech NASA project. I better just stop thinking and start doing!

I'm sure you will get more precise advice from others but AFAIK that cavity is only protected by the screw on splash shields at the back of the wheel well. In other words if that isn't working well it could be wet and nasty in there. Speaker cones don't survive long under those conditions. A neat and tidy repair will take a bit of skill but you will still have to remove the splash guards to get to the back for finishing and anti rust treatment.

Hey Derek, thanks for the response. When I was looking in there I did see some fasteners that looked to be passing through to the inner fender. I did think "How odd, why isn't it welded together rather than screwed?" It didn't occur to me that there may be a removable panel. The inside of the cavity is somewhat dirty and dusty but it doesn't look like there has been any water intrusion.

My plan was to trim up the speaker holes so that they are a more regular shape like a nice clean circle or rectangle with rounded corners or whatever. Then I was going to cut out a sheet metal cover that can be screwed on over the hole with a homemade black foam gasket sandwiched between. The thought was that being able to access the inside of the cavity could be beneficial in the future. Why? Heck, I don't know. Now I'm thinking I don't have to be all that particular about how well the cover plate is sealed against the body panel.
--
Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

As the cavity is dry and dusty it's probably in your best interest not to disturb the splash plates. I think I would go to the option of tidying up the hole and using a cover plate using screws and sealant. The strengthening ribs on the panel won't help you to get a plate that is completely flush but using a sheet rubber gasket or closed cell sponge will help. It will be covered in carpet anyway. Spraying the inside with rustproofing cavity wax a good idea. Water in here can cause a lot of damage to the A post area. As it attacks from the inside, by the time you notice it the damage is serious.
If in the future you have to remove the splash guards, that is probably the time to do a more permanent repair to the holes, but worth removing the plate now and then to check if all is well.