Tools

Just a little note about tools. There are a few tools that I think are very helpful if you decide to build your own trailer. My favorite is an impact driver. It is great for removing older screws and putting new screws in. Some people may just want to use an electric drill/driver but they aren't as good as the impact driver. I use a Ryobi with a 18 volt lithium battery. great stuff.
When you get ready to build the frame a pocket hole jig is another great tool. It allows you to create super strong joints without worrying about the screw heads sticking out.
If you have an air compressor a nail/staple gun is useful to staple the siding and paneling.
And then there is the hand tools such as a hammer, screw drivers and crowbars. When you are demoing an old trailer sometime the only way is to pry it apart with a crowbar.
Most of the time old trailers are going to have square head screws. Some people will try to use a Phillips head but it won't work. You may get one or two but for the most part it is going to slip in the head. Get the right tool.
If you aren't trying to save the part you are removing, you can use a saws all. Those thing are extremely good at destruction.
A good tool will always work better than a cheap tool, but sometimes if it is only needed once a cheap tool will do. You can also look at renting something if you need it. Home depot has a nice tool rental program. I hope this is helpful.