Is there anything to worry about?

We plan to ride and walk. There would be 3 possibilities:

1. Carry frameless backpacks in baskets. Wasted space and not very good on the trail
2. Use the Ortlieb carrying system. The same disadvantages as above
3. Use our backpacks instead of baskets. Ideal for hiking, but not sure if they will travel well by bike.

The idea would be to tie both backpacks together with a short ribbon and put them on the back rack. This would give something that would look like saddlebags for riding. We would add horizontal straps tied to the bottom of the rack to prevent forward and backward movement.

Probably, we will have to put something up first. On the back shelf, and on top of a pair of backpacks, so that there is enough space for switching.

If I missed the obvious "no-no", please enlighten me.