Newbie - what is annual maintenance for a TT ???

You don't have to be an expert to perform most maintenance on trailers. The most valuable skills you need to possess is being observant. You can catch and repair most problems before they turn into big problems that require big money and specialist tools. If you have a basic working knowledge of plumbing, carpentry, electrical, mechanics, etc and are motivate to do things yourself then there's a good chance that you'd rarely have bring your trailer to a dealer for work. However sometimes you have to realize when you'll be in over your head and bring it to the pros instead of making a mess of things.

Most things on a trailer can be maintained or repaired with basic hand and power tools. If you wrench on your own car or make repairs around the house then you'll start to see the similarities between those systems and your trailer. A willingness to ask questions is also a valuable skill. The internet can provide a wealth of information. Often times you can ask a dealer or the manufacturer for guidance. Surprisingly plenty are willing to help without taking your money. But as K9 HANDLER said, don't blindly accept the advice. Even the experts are wrong sometimes. After a failure don't look to just repair or replace, but improve the failed system.