Best tool to remove old paint and gunk?

For removing paint I prefer using the most caustic chemical/solvent based paint remover I can find. Not exactly eco friendly but much faster than any other method I know of. Any abrasive method I have tried took more time than I had patience for.

I have not yet had to remove silicone from a vintage trailer so can only speculate.

The best tool is going to be your elbows... Most trailers have more than the original coat of paint on them and many were done with house paint. Sometimes more than once. House paint is the hardest to remove. Nothing seems to want to strip it short of sanding it off. Silicone is a whole nuther story. And that story is why we all hate it so much. We cringe when someone even brings it up. Although we pride ourselves on being a goop free zone we have to deal with it all the time. And silicone is not a fun thing to deal with. Depending on the surface and how you want it to look eventually you are going to be looking at everything from razor blades to wire wheels and other implements of destruction. No one thing works for all of it. You will end up using a variety of things to remove paint and calking from your metal. Just be careful, read directions and wear protective eye wear and clothing.