Simplest plan is to just replace it every few years. They don't cost much, and any DIYer can do the R&R.
Unless it's an old trailer with parts no longer available. In that case keep the trailer in a barn and keep the plastic dome covered with UV-proof covering of some sort.
Grumpy ole man with over 50 years towing experience. Now my heaviest trailer is a 7,000-pound enclosed cargo trailer, RV is a 5,600 pound Skyline Nomad Joey 196S, and my tow vehicle is a 2012 F-150 EcoBoost SuperCrew.