Need to upgrade Cisco devices over DMVPN but struggling

Hey all,

Trying to write a script to copy new code to devices out in the field but it is going poorly. TFTP copies always throw in 0s (!!!0!!0!!! for example) and never complete. SCP will work fine but takes 2+ hours. I tried increasing the block size but no dice. I am not maxing out WAN circuits on either end but understand I am at the mercy of the internet. The only thing I am thinking about doing is doing it overnight but does anyone have experience with this? I know it takes ~30 minutes or so over an MPLS connection but 2+ hours is unbearable