All,
I'm currently working on restoring a passenger coach. We are replacing rusted-out metal on the roof edges where it was riveted with hot rivets. Unfortunately, we can't come in from the back. So what alternatives exist (similar to hot rivets) that will accomplish the same objective and look as close as possible?
Thanks.

Assuming you can get a wrench in there but don't have enough room to buck up behind the rivet, you can buy a rivet-head bolt with a knurled shaft, like a wheel stud. Use a good seam sealer under the head.

There are many applications of round head machine screws which get the slots filled with bondo after application. I have seen this method even used by railroads when they were maintaining old passenger equipment. But small hot rivets are easy and fast to install and should be used when ever possible. Since they fill the hole completely, they work better than threaded fasteners on railroad equipment.

Another alternative is to use Huck bolts. They make a version with round heads that are really more like a large, very strong pop rivet. And they are inserted and pulled from the outside. The problem is the equipment is pretty specialized and can be expensive to purchase, but sometimes places that supply the Huck bolts will also rent you a Huck gun.

We had used drill-taps, and socket head, round head screws with the socket then filled with bondo. Goes pretty fast.

What Kelly has offered is about the only way to approach this. Along with this you can find these fasteners with a rubber washer already bonded to the head for a rain tight seal.

I've never seen Button Head Socket Cap Screws with sealing washers... all the self seals seem to be hex heads. Got a source?

start with the old standby, McMaster Carr. They have these products and sealing washers metal backed and not. https://www.mcmaster.com/sealing-screws. Google search sealing screws and you will find a lot of configurations and head types

There is also this type of security bolt. I've never used them but thought they would be ideal for replicating a rivet head. A little touch up with an angle grinder and you would be done and not have to fuss with bondo.

https://www.losspreventionfasteners.com ... ork-bolts/

I don't see them in Mcmaster, however if you contact them with a link to a specific product they can almost always get it for you.