I’ll start with the disclaimer that I’ve never actually been touring with a unicycle, but I’d really quite like to! – not at the level of Ed Pratt or Becky, but some muni packing/touring type gravel thing in the wilderness for a few days… (!)
For some time now I have been toying with the same idea as you – I’d really like to build my own touring frame (CrMo) – I’ve got the ability and tools (he said arrogantly 
) but I just seriously lack the time at the moment to do anything about it. However I’d really like to go touring on a frame I’d designed and built myself on a wheel I’d built myself – that appeals very much.
All my thoughts have centred around a V-frame design, primarily for its load carrying capability, rigidity and ability to resist twisting from pedal torque with a good handle setup. The latter also lead me to consider using a bicycle saddle rather than a unicycle one.
The type of saddle which Vogelfrei80 experimented with in this thread looks pretty interesting:
Handle saddle cushion ideas - #23 by Vogelfrei80 .
You’ll also see Hammer has a similar saddle in his setup in the Handlebar thread:
post your homemade handlebars here! - #460 by Hammer .
and of course toutestbon’s Flansberium V-frame with a bike saddle:
Post a picture of your unicycle(s) - #580 by toutestbon .
and
post your homemade handlebars here! - #461 by toutestbon
JimT also did a thread on a noseless saddle, but I was not so keen on that idea, probably since I quite like narrow bike seats…
Noseless Unicycle Saddle .
I tried someone else’s bike with a Selle SMP saddle recently and I really quite liked it – I have been a fan of Brooks leather saddles for a long-long time (Swallow, Swift, B17 etc) but could be converted to the Selle one.
Anyhow, the frame idea would probably integrate some rack and bag setup as used by the likes of Ed and Becky into the frame structure rather than being attached to a seat post (Ed has a new uni-packing adventure coming soon on a 29"er so it will be interesting to see the the details of his setup there and compare with Becky’s European Divide setup).
I need to start sketching stuff out before starting some drawings – however at the moment it is still at the stage of daydreaming when I need to take my mind of work when things aren’t working – I am an expert at procrastination at least!