Before you install it in a camping site, I'd suggest to have an interior pressurized leak test done. The leak test will uncover even the tiniest pinholes. The age and stated use of the trailer makes this test appropriate.
Sealtech is one commercial franchise that does these tests or it can be a DIY job if you can find a friend with a large enough blower like a squirrel cage or lawn leaf blower. You can search the Forum for more information on the pressurized testing.
When/if any leaks are found, you can seal them and then your little get-away on wheels will be safe and secure.