If you are like me, and do not really care about trying your luck scavanging the two open world maps picking up refined resources (or getting lucky with some red cargo containers), then know there is an easier soultion to obtaining materials needed for construction, especially on the last tier for each platform:
Once you get to a certain point in the game, you will unluck this game mode where, basically, you invade another players FOB and steal stuff, and soldiers. There is also an achievement for the activity:
Each platform offers up different rewards that scale based on the number of platforms built, and the level of security the enemy player has currently arranged. For example, if you are in need of Fuel Resources, the infiltrating another players Support Platforms are what you want to do. If they have 1 platform, then on completion you are garunteed ~4500 fuel resource. If they have 2, then that number can double, and so on. (Also, on 2 and above, you have the option of extracting via fulton cargo containers with other resources).
Each platform offers up different resources, and are structured differently, however once you learn the layout they can be easy to run through.
Questions, corrections and neg vote justifications below.