Help with Hardware on Horse Trailer?

I have a horse trailer with swing out door with handle. The handle started to rust and the bolt came off the handle and there is no way to close it now. This week I have to trailer my horses into the vet and need to use my trailer. My question is what is the best hardware to use to put the handle back on? I do not want the bolts to loosen and have the door swing open while driving. I have tried researching but cant find any answers. The end of the screw needs to be flat enough so I can close the door shut. Thanks to anyone whom can help!!