Yes, that I'm fairly sure is an M116A3 trailer frame under the flat bed, which is the basis for the M101A3 trailer. I have an M116A3 frame with an M101A2 box on it and an M101A1 trailer as well.
The A3 versions have the drop axle as shown in your photo.
Good basis from an expedition trailer so long as your tow vehicle is up to it. In my opinion a JK or so is up to it. Your trailer should weigh about 800lbs less the flat bed according to the plate on my M116A3. Add maybe 200lbs for the flat bed. (The A2 box weighs 575lbs, a testament to its robustness.)
I'm building my A2 for the purpose now, but I could see the one you pictured being as good a base or better. Some top mounted "under frame" truck boxes on the sides for storage, maybe a utility box for more, rack for a RTT... good to go...
JPK