Those latches will work in terms of holding the door against the gasket, but they will kind of defeat the purpose of installing a lock in the first place since you'll only be able to open the door from the inside, which effectively locks it anyway. If you still have the original three-point latching mechanism, perhaps you can put it back and then install your lock somewhere else. If you've already thrown it away, perhaps you can install
a replacement three-point latch kit like this one.
On my bus, I kept the original three-point latch but cut off the outside handle and riveted a patch over the opening. This way, the door can only be opened from the inside (so it's secure) and it can be opened easily in case of an emergency where I need to get out of the bus quickly. Of course it can't be used as an entrance this way, but a rear door is not really a practical entrance anyway.