Hardly anything on a yearly basis. Less than my vehicles. I may buy a tube of caulk to touch up some caulking. But other than that there's really not much money spent on maintenance on a yearly basis. Some will wash their roofs with a cleaning product, but that's relatively cheap.
The biggest expenses are going to be all the stuff you think you need for the trailer that you'll buy. I'm always fiddling around with something so I'm spending money on some project. Most aren't do or die projects. More like upgrades to make things easier or better.
You'll need tires every 4-5 years. Re-pack the bearings every two years for me. If you have someone do it then that would be $100-200.00. I do mine so it's just the cost of seals and grease. $20.00 or so.
On the other hand if you're the type of owner that takes their RV into the dealer every year for a checkup and winterizing then I'm not sure what the yearly costs would be since I've never done that. I know winterizing runs around $50-75.00 depending on dealer. It's good to adjust the brakes yearly too. ($$?) Not sure about the inspection costs. A call to any dealer would give you an estimate.
Best thing to do to save money is to learn how to maintain it on your own. Most of the maintenance besides re-packing wheel bearings is fairly simple and easy.
Usually all the instructions you need can be found by Googling it and finding a YouTube video. There are some really good instructional videos done by dealerships or RV suppliers that will help you.
