fixing / upgrading a trailer is more difficult than doing a Home..
its a moving/bouncing House... on wheels.
materials are harder to find and cost a lot more.
and IF you do not know how or can get the skills cheaply... call it a PASS.
and your questions suggest you do not.
from my past experiences.. unless you plan on this to be a learning/training experience for you.. you will end up doing it twice.. once to learn, second time to do it correctly.
your trailer, your money, your time, your decision
best of luck