Putting more into my travel trailer than it's worth!

all depends if you plan on keeping it or using for a longer period of time. Used trailers are worth more if sold privately versus trade in.
Brakes and tires are a normal wear and tear items including battery. The genny can be moved to another unit if you sell the Prowler.

The value can be determined by calling a dealer most will give you the value from the NADA books they use. You may be able to check NADA on line for value.