If you are looking fo a cheap job (cheap is emphasised,
no flames please) you can paint aluminium with an ordinary
roller and household gloss, eg Dulux enamels, I hope
Dulux is recognisable in the USA.

Yes, I do know that if you're going to paint Alu properly
then you use epoxy etch primer and a decent topcoat,
but the raw materials alone are still going to be about
400ish dollars, trailers have a big surface area.

Compare this with 10 litres of household gloss, no
flames please, this is a cheap suggestion, it works
and has lasted for 5 years so far.