Who makes the lightest 50 amp bunkhouse trailer?

I wouldn't let the 50A requirement dictate the trailer; that's the easiest thing to change. Find one that is within the capabilities of the tow vehicle, has a layout you like, is a good price, is well made, etc. Then, if it happens to only have a 30A service you can easily swap the breaker box and the power cord. Or, have an RV shop do it for you.