Quick Fix for a Springy Deck

I built a simple and small deck for the area in front of my vintage camper, and cut some corners to keep costs down and simplify the build. The result wasn't good enough. The span of the cedar boards ended up being too great, and created areas of slightly unsettling springy-ness as you step on the "wrong" part of the deck.
So I'm implementing a super simple and solution using some reclaimed 2x4s.
If you have any questions, please feel free to comment.
Thanks for watching!