Using a trap seems like an good option.  Traps made of coaxial cable generally work  well even though the Q isn’t as high as traps with discrete L and C components.  I’ve made and used them in dipoles, but not in a vertical.  

There is an antenna called the Battle Creek Special that was loaned out to several DXPeditions.   I think it covered 160, 80, and 40 using coax traps.  It was generally set up as an inverted -L.  

I’ve made fan dipoles from ladder line and they work fine even though many would say spacing must be 6 inches or some other arbitrary figure.    I’ve thought about making an inverted-L using <>65 feet of ladder line and adding a wire to one side to resonate on 160.   Connect the two ladder line conductors together at the feedpoint.  It would be like half a fan dipole.   It might  take several adjustments to get it right on both bands, and if using a tree, that could be tedious.   You could also just use a second wire  as the 80M radiator.

My 160M inverted-L has ONE radial.  It definitely needs a few more.

73,

Dennis/RZ