Those 40 amp fuses are your ONLY reverse battery protection.
Most DC stuff will work with a reversed battery (lights don't care for example); HOWEVER, some things care A LOT; like your heater, fridge, LEDs, anything solid state, etc.
Be VERY happy if you were just inconvenienced. I accidently reversed the battery cables in my Yamaha generator when I replaced it and is cost me almost a 5 hundred dollars to fix it.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW