What are the 2 40A fuses supplying? If each is for one leg and your trailer is a 50A service max, then someone messed up. Any trailer/RV I am aware of has a 50A max service. Therefore 40A fuses on each side are way too high for your application - what does the mfg. want on each leg? I think you need to know which side of the panel the items in use were being operated through, if they are fused correctly - did someone boost the fuse size to correct an overloading condition - ILLEGALLY!?, and what load was applied to the entirety and each leg separately of the system - hot water, AC, Vacuum, lighting, fridge, tv, booster, etc. Good luck.
2011 Chevy 1500 SB 4x4 5.3L w/trailer tow
2013 Zinger ZT23FB
Reese Weight Dist. w/friction sway control