I'd probably go with Diafine if I could get it.

Make a 1 litre batch (or your tank size plus say ~30%) before you go. Then you'll have 2 x 1 litre bottles (A and B solutions, reusable), plus enough fixer. You won't need to worry about temperature, and your timings don't need to be too accurate either.

Another alternative, already mentioned, is Cafenol. You can easily get whatever you need on the road.

Have fun!