I am a Marin owner (Yes, I have a beard) and a frame bag wouldn't fit my Mount Vision frame. But even if it did why would that be preferable to a "horsey" style saddle bag setup?

I'm envisioning something along the lines of a drybag lashed either side of the top tube, possibly with some sort of webbing support system. Is there a good reason I haven't seen this setup before? Because I really can't think of why not.

keeps the weight more central and lower down, better stability, bit of an arse if you've got to carry your bike though

as to your idea, i think the main problem will be leg rub

It would get in the way of your knees?

There is a surprising amount of clearance for my knees. Perhaps I'm more bow legged than I think.

my epic designs frame bag dosnt rub on legs,keeps the wieght down low and balanced…but you cant shoulder the bike if heather louping etc…have a look at the handlebar and seatpost bags available from epic designs etc,maybe all you need to carry a bivvybag,3/4 mat,sleepingbag,with them and an allday backpack for a stove/food you could hump enough for 2-3 days without the framebag…