I have the same problem. I have found that by using battery cleaner to clean the fluffy corrosion off and battery terminal protector after cleaning the fluffy corrosion off, it works fairly well. I have had the same brace between the house batteries, where the battery hold down strap contacts it, corrode a number of times. But the cleaner/protector step minimizes it, and I have to re-do it about every six months.
One thing I have found helpful is to minimize the water in cleaning the battery compartment because it tends to spread the acidic liquid venting from the batteries.
Instead of washing, I dust the batteries and the compartment regularly with a swiffer duster. We first dust the inside of the coach with the swiffer, then I use it to dust the batteries and wipe out the excess venting before disposing. If I see some corrosion I'll clean that and carefully flush only that area with water, dry it off, and put on the battery terminal protector. Seems to work fairly well.
I got both the battery terminal cleaner and protector at an auto parts store; just matched the same brand. I think NAPA works best, but mine came from Kragen.
2019 Winnebago 22M
2015 Jeep JK Rubicon
Former Owner, 2006 Alpine Coach 36MDDS
Former Owner, 2005 Tioga 31M and Arctic Fox 22GQ