My opinion is that a lot is going to depend on the severity of the oxidation on your trailer.
I have recently finished polishing out the gelcoat on my 35 year old trillium
(from 220 grit wet sandpaper in some spots -> 400 wet -> 800 wet -> farecla profile 100 coarse compound -> farecla 300 polishing compound) the whole process was fairly time consuming and I would only recommend it to someone that would find some satisfaction in the process, for me the work was repetitive but relaxing.
Before I did the work: waxing the trailer or using gel gloss or even a bit of tutlewax compound and then wax would get a shine but it wouldn't last a month. something about the microscopic roughness of the surface speeds up the deterioration of whatever wax or protectant you put on your trailer. I understand that poliglow or vertglas seals over the oxidation with a layer of some kind of polymer but if it was me I would consider taking some of the oxidation off first to improve the underlying surface (maybe a quick pass with 800 wet sandpaper).
edit to add:
I know that these products have cleaners that are supposed to remove the oxidation, what i found is that as the gelcoat gets oxidized it becomes softer and slightly porous in the badly oxidized spots, it takes more than a chemical cleaner to improve this. In our case I had to do some aggressive sanding to take some material off and expose the harder, more solid undamaged gelcoat underneath.
I am not trying to discourage using vertglas or poliglow, i just think that you'll get a longer lasting result with the right kind of prep in advance.