It may not be possible to prevent the download from timing out. Even if there is, there's way to little information in your question to diagnose why it's timing out. I've transferred files > 100GB over SCP, there's nothing about SCP which implicitly prevent this.
However, while the timeouts are annoying they should't prevent you downloading the file, as long as you can resume the download after a timeout. SCP can't naively do this AFAIK. However rsync can. What's more MobaXterm does include rsync on the command line and rsync can be tunnelled over SSH.
In MobaXterm, open up a new tab using the little "+". You'll presented with a bash command line implemented in cygwin. Your windows drives can be found under /cygdrive, eg: c: is /cygdrive/c.
There's a discussion of using rsync for resume support here: https://stackoverflow.com/a/20860920/453851
Short version is:
rsync --partial --progress --rsh=ssh user@remote_host:remote_file /cygdrive/c/Users/user/Desktop