Depending on what you plan to store do you need ventilation? I had a shipping container at work that I used to store stock (heating fans in cardboard outers) over winter and all I did was sheet the roof with a marine ply board and then tarp the roof. I overlapped the tarp so it sat over the roof onto the upper walls (sides and rear) and added a trim to cover the tarp. I used that shipping container for 12 years and replaced the tarp once in that time. And never had so much as drop of water even in heavy rain.

For those exhausts to be even slightly effective they need a wall vent to induce a draft, otherwise they aren't doing anything. But..I mean they aren't the most effective even when installed properly so..🤷‍♂️ since it's a storageshed maybe you don't care much about moisture inside? I guess it all depends on what's going to be stored in there, and how much work do you want to put in?

To address your other question, assuming it's sheet metal just cut the vent out, get yourself a piece of 13"x 13"(or bigger, just get a piece 1" bigger than the hole), a box of self sealing sheet metal screws and some waterproof caulk. Should do the trick and should keep out the water.

I’m going to be storing electronics and furniture (plastic bins / wrap) — ideally it would be moisture controlled. I live in a desert, so there’s that working in my favor.

I’m okay with fixing the venting, but not sure of the best way to patch the old hole on the roof. (Buy a sheet of metal, screw it in with roofing screws, silicone caulk the seams?)

Exactly that. Just make sure it's waterproof caulking and the screws are self sealing.

In that case I'd vent it properly and make sure the whirlybirds are actually functioning(they often dont). Also you'll want to make certain the rest of the sea can is water tight(as best you can) if it isn't those roof vents won't be enough to keep excess moisture out.

Could you weld a thin steel plate to cover hole in roof

I know pretty much nothing about welding — is it difficult to do?

It's probably not where you want to learn to weld. Metal, screws and caulk will work just fine. I would use a seam sealer caulk for automotive use.

I’d use rivets , smooth on both sides

I’m thinking I do need the vents. I live in a desert where the UV heats the interior of the container significantly. (Above 130f).

I’ll be storing electronics and furniture in there and don’t want them subjected to moisture or high heat.

The exterior plywood is a good idea. Kind of like making a miniature roof for the roof of the container?

Does the automotive caulk hold up more than roofing caulk?

I’ve never used a rivet gun before 😅. Sounds fun, but more work than roofing metal-to-metal screws?

What would be the benefit? (Other than aesthetics)

Today was angle grinding off the existing roofing asphalt. That stuff is a mess, but fortunately got it all off.

I picked up a 12” x 12” gable louver to put in the rear side of the container (where it can catch a draft). The one I picked up has a mesh grate in the rear of it, but I’m going to find a way to add foam or something to filter the air intake. (Tape an air filter around it?)

I also picked up a replacement 12” whirlybird because the previous one wasn’t installed correctly (and the whole assembly was busted, including the bearings). Get to take that on tomorrow!

Also picked up some tek roofing screws, and silicon roofing sealant. (Tho another comment suggested automotive sealant?)

Thanks for the help!

Oh wow then my tarp idea is definitely not a good idea. That would make it worse in fact.

You'll definitely need ventilation with those temps. I'm no expert on vents, sorry.

On the roof though, someone else mentioned about automotive caulk and that's a great idea as it functions metal to metal. Most roofing caulk doesn't bond well like that. So that's a good suggestion. You preferably do want to cover the roof so that water does not sit in the gullies as that will be a problem down the line. Marine ply will work but in that heat I'd seal it with a heat resistant roof covering, and if you are DIY handy I'd pitch it to one side to create a run off. But be careful that you don't inadvertently drain water down the outside as that will again cause you problems later on so overhanging any roof would be preferable.

Edit: using a heat resistant roof felt would negate the need for marine ply. That's 4 times more expensive than traditional ply.

Yeah, I’m already seeing signs of rusting from past rain. Thanks for the suggestions!

It's made to help seal steel pieces together. Look at the 3M brands.

Ok, I did a bit more reading into using rivets. Main question is: will a 3/16” aluminum rivet be weatherproof, or do you need silicon over it?

Nice, I found the 3m dynatron seam sealer at autozone nearby! Thanks for the pro tip!

Screw done a pc of steel or plywood and use this. https://www.paintsupply.com/product/architectural-specialty-coatings-one/roof-driveway-coatings/roof-coatings/2-gallon-gaco-gp1525-2-gray-gacoroof-silicone-roof-patch/?utm_source=google&utm_medium=surfaces&gclid=EAIaIQobChMIgNKxjvrr_AIVxd7ICh3tUAIMEAQYAiABEgISw_D_BwE It’s expensive but it’s designed for applications that you’re describing

I want to mention the temperature issue since no one else has yet.

What color is the container? How hot does metal sitting in the sun get where you are? I'm in the Seattle area and two summers ago, we had some 100+ degree days which is really rare around here. I had the fortune of temporarily storing some electronics outdoors for a bit in an area that received direct sunlight for the second half of the day. Black computer cases. On our 104 degree day, I noticed the plastic on front of some of the cases had warped. On our 108 degree day, I measured the temperature on the surface of the cases at 170 degrees. So while that didn't warp the plastic, the cases with metal directly behind the plastic did warp the plastic.

So, just be very aware of the potential temperatures and store your electronic accordingly. Possibly a good few coats of paint designed to reflect heat (the kind used on the tops of school buses) would be a good idea.

Ships are riveted together, so it can be pretty damn weatherproof. Screws and rivets will be about the same work but with screws, what are you going to do about the pointy end?

The container is painted red — the top is painted white. We regularly get up into the 90s, but the UV is intense here, so metal heats up quite a bit.

Good points to consider, thanks!

Yeah, I went ahead and got a rivet tool. Going to go that route — thanks for the suggestion!

I just skimmed so forgive me if I'm being repetitive. Coolseal is a brand name for a mastic that I have used to stop leaks in mobile homes. Obviously it's designed for metal and I put it on with a paint roller. It would be worth consideration.

It worked out really well! Thanks for the suggestion!

Happy to help!