How to change font in appImage

I have 2 AppImages (vlc and kdenlive). They work great and I really like the appImage concept, however, the default font size for both is tiny and makes using them difficult and annoying. I know I could contact the devs of each particular appImage and ask them to update their default font settings, but that would be ridiculous to do for every app I want to run, plus I want to be able to control the fonts for everything on my box. Everything else on my computer conforms to the settings I have set - except appImages. This is a pretty big problem for me and I’m hoping there is a way I can either: access a config file for the appImage and set fonts directly, or find a way to make the appImage respect my global settings. I’m running ubuntu 18.10. Thanx