M105 weighs about 2700 lbs empty. Mule weighs 870, + supplies weigh ? Figure 4k lbs to make it a nice even number.
Most states require any trailer over 3000 lbs to have brakes (for good reason) so you're technically breaking the law. There's a few exceptions where the law states as low as 1500, and as high as 10,000
but for the majority of states/municipalities it's 3000 lbs.Don't take my word for it, look up the law where you intend to travel just to be sure. Google is your friend.
I see unsafe trailers on the road every day. Realistically, non-op trailer brakes are probably the last thing you will get pulled over for because it's not like a cop can see your brakes (or lack thereof) from the side of the road. DOT enforcement is after commercial drivers and unlikely to care about a "little" truck. Will you get pulled over for it? Doubt it.
BUT.... remember that we live in a litigious society. If you are ever involved in a serious accident whether or not it's your fault, there's a high probability you're also going to get sued. If your trailer wasn't completely safe/legal at the time of the accident, you can kiss your insurance policy goodbye. No chance you'll win a civil suit if you were the one driving an "unsafe" vehicle. Doesn't matter if you are the world's safest driver; if your vehicle doesn't meet minimum legal requirements, you have zero defense against a lawsuit.
So to answer the question:
You can do it. I wouldn't do it.