The handle pivots two bars attached to it that engage slots on the frame on either side of the trailer and one in the lower frame when the handle is turned. There is no way to force anything without damage. I'd call a lock smith, or maybe watch some youtube's on lock picking. Once you get it open you can replace the handle. Vintage Trailer Supply has the handle and a replacement locking cam system in you need both. (Baggage
I would get all the other compartments keyed the same so you only have to keep a door key and a compartment key on your key ring. Any good locksmith can do that for a small charge in addition to whatever he charges to open the compartment. Probably be money well spent.