Here is a statement from a brocure on the oregon dmv website
Number of Vehicles in combination without
special permits:
A vehicle may tow only one vehicle or trailer in
Oregon (a two-vehicle combination ORS 818.110).
Some states allow towing more than one trailer or
vehicle by non-commercial vehicles. Permits are
not allowed in Oregon for towing more than one
trailer or vehicle except for commercially titled and
registered vehicles.
However,it appears that this "brochure" is written for oregon residents, and hence that may be why it doesn't show anything about a pass through allowance.
I tried including the link, but for whatever reason, RV net comes back with "connection timeout" whenever I try that.
Now, regarding the "idaho tote" does oregon consider it a second trailer? or does oregon consider it part of A trailer. It's a rigid connection, but can be disconnected.
I'll leave that determination to oregon DMV to address.