I have been at this too. Thanks for the vote on Trimble's app; I find Orux overwhelming to use, and the Mobile Atlas Creator underwhelming. Orux has alot of options, and it will probably be fine once I get up to speed, but the atlas creator is lacking - it should tell you what the max download is so you don't have to keep trying smaller and smaller guesses... :(
I have also looked at many other free options and one other paid (w/free trial) but never used any enough to say if they are good enough. I'm surprised Google dropped their My Maps Editor, and does not support speculative downloading of tiles to cover areas w/out cellular service (particularly with route planning on My Maps).
A Garmin rep told me that he knew of no programs that could convert their maps for use outside of Garmin software - but he didn't tell me they were against that, so if you are writing an app, have it read Garmin Topo.