I haven't seen this mentioned here before, so forgive me if this is common knowledge.
An ATX desktop computer power supply is a very solid (and cheap, or free) option for converting AC power into DC for trailer use. I've converted a few ATX units into bench power supplies for my garage and other purposes over the years, and it seemed like a reasonable thing to do for the trailer as well. After over a year, the thing is still doing its job without any complaints. 120 VAC in, 12 VDC @ 25 A out (amps out depends on the unit, but 20 - 25A is most common), and very stable because desktop computers are fussy about power quality. Those specs are beefier than RV-specific converters that cost hundreds, and used ATX supplies are incredibly plentiful wherever you are.
I know this forum is often suspicious of non-commercial (DIY) solutions for electrical things, but I thought I'd throw it out there anyway. The conversion process is easy (and very, very well-documented on the web), so if you're looking for a cheap way of getting high-current 12 VDC into your trailer when 120 VAC is available at a campsite, from a genset, or in your yard, check it out.
S