You didn't take into account the abuse the batteries suffered on the dealer's lot before you bought the RV.
Bulk and absorption modes are not the same thing. If the load of charging current by the battery bank is less than 10 amps in bulk mode the converter is smart enough to switch to absorption mode, and then to float mode when the battery is fully charged. Adding a separate charger with a different charging profile in parallel to the converter will not only affect how that charger operates/reacts to battery voltage, but also affect how the converter charges and may not accomplish what you are trying to do.
Good luck with your experiment.
Ted & Melinda
2016 ACE 27.1
2016 Chevy Sonic Toad
2020 Chevy Colorado Z71 Trail Runner Alternate Toad