I did Air Conditioning repair for many years in the south, including RV AC units, but haven't in 30 years. Low freon can/will cause the coil to freeze. Unless the unit has a leak, the freon would not normally be low and it doesn't wear out. If there is a leak, usually you will see an oil stain on the copper (or aluminum, YUK) line or in the coil itself. Much of this is hidden and not easy to access.
The number one reason for the AC to freeze up is the evaporator coil (the coil that the inside air blows through, not the outside one) is clogged with dirt/dust/lint/etc. This causes the air flow to be reduced enough that the coil will ice up.
The filter that comes with most RV AC units is crap and let's way too much dirt get through. But, it works well enough to get the unit out of warranty
I think the evaporator coil needs to be cleaned. The problem, if memory serves me, is that coil is kind of hard to reach. As someone suggested, you can drop the ceiling grill. Then use a flash lite and look up in the dark cavity and see if you can see the coil. If you google "dirty RV evaporator coil" you will have a bunch of links to videos on what it takes to clean one. Be careful, it is almost never as easy as the videos suggest. If you click images across the top, it will show some pictures of where the coil is.