depends what the purpose of the added lenth would be. Is it just for loading/unloading or would the rig actually be farther back on the trailer? My concern is that a 16' trailer has the axles in a certain spot to have an even load with the rig centered on the trailer. Now you would be adding a 2' extention and possibly havin the rig 1-2' farther make, making it tongue light, which would fish tail all over.
As far as the actual "can I do it" from a fabrication standpoint... sure, just brace it and where the 2 C channels but up against each other, brace with a fish joint like this <>
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