Outsyd--- if your hitch can support 150 lbs. You don't need a trailer. Just mount a box to the hitch.
with the rear frame and cowling it may or may not be possible to mount a small receiver for a trailer hitch .... this link http://www.motorcycle-superstore.com/41775/i/khrome-werks-1-1-4-receiver-trailer-hitch shows one for standard motorcycle that shouldn't fit an Elio but can illustrate what I'm referring to .... one could be used to mount a hitch for a trailer or a small carrier .... with a carrier my concern would be the force exerted on the Elio's frame as the rig bounces down the road
Jim