TreeSeeker:
This is starting to get beyond the scope of my knowledge and experience. It's one thing if pushing my existing limitations causes a problem for me personally. However, I'm very resistant to the possibility of causing problems for others. This is the reason for my frequent use of caveats, such as usually, typically, in general, and so forth. (As is, I still make enough mistakes to be personally disheartening.)
I recommend contacting Progressive Dynamics customer/technical service and discussing your concerns with them.
Having said that, there are a few things I can reasonably state.
Power supplies and multi-stage battery chargers are very different. Because they are similar in function, the significant differences are easy to overlook. (This is precisely where most people encounter problems so you asking questions is noteworthy and commendable.)
Modern power supplies produce regulated and filtered output at a steady voltage, provided they are good units designed and manufactured by a reliable company. (Five caveats in that statement, put in italics to make them noticeable.)
Multi-stage battery chargers sense the state of the battery's charge and vary their output voltage in response to the charge level. The initial bulk stage is at a relatively high output voltage. As the battery approaches 100 percent charged, the output voltage is reduced or pulsed off and on. (Two different techniques effectively yielding the same result for the battery.)
At the risk of oversimplification, voltage is pressure and current (amps) is volume. This is the basis for using water and pneumatic systems as a generalized analogy. (The physics involved are significantly different, with changes in the battery's internal chemistry adding to the differences that cause the analogies to fall apart when you dig deeper.)
I'm willing to bet Progressive Dynamics converters use the battery as a back-end buffer, to supplement the power supply's output when load demand exceeds the power supply's capacity. This is similar to how an engine's electrical system works. (I'd need to dig deeper to verify this assumption.)
Quite likely, the converter's output to the coach circuits is regulated and filtered to a steady voltage, regardless of what's happening on the converter's back-end.
An alternative for you is to use your existing power supply and a separate multi-stage battery charger. This would involve using a switch or relay for an exclusive-or for electrical source. (Battery OR power supply but NOT both at the same time.)
My main concern in this alternative is the effect of voltage drop/spike during switch-over.
