Going through some related items to products I was looking at, I came across this charger. It doesn't list any of the actual specs, only that it will charge batteries down to 1 volt. At $180 it's cheaper than some of the other options I've seen in the past, doesn't have to be permanently mounted, and will charge the batteries then maintain/float charge them when done.
As we've gone over above though, it's still better to charge individually if possible, but if you have a dual voltage generator in your truck, and just want to keep the batteries topped off when not driving, this seems like a decent option.
24 vdc Low current maintenance charger
graywacke.net
This company also makes the NATO slave port adapters to use with any other type of 24V charger (it's also the company that manufactures the slave cable for the NOCO 26000 charger that Black Dog used to sell before NOCO discontinued the 26000)
graywacke.net