I called Tripplite about upgrading the inverter/charger from the 750 to the 1250 and was told that the 750 & 1250 are NOT suitable for charging Lithium batteries. I also found out that you cannot charge lithium batteries directly from the alternator, as they will try to draw too much power from the alternator and fry it. I ended up getting a Renogy 2000 watt inverter/charger (which is very heavy & large) then when I did upgrade to Lithium Batteries, got a Victron Orion DC to DC charger for charging from the alternator. I have been happy with this expensive upgrade until recently. I fried the power in connector that provides power to the charger side of the inverter. I used the original one that was installed by Roadtrek which is 14 ga wire. Now I need to upgrade the power feed to inverter/charger. I need atleast a 12 ga wire to feed the charger with a new breaker that I will connect to the power transfer switch. I will also add a breaker to the inverter side (120v output) to prevent any problems there. I currently only run my coffee maker and an outlet charging or running computer and other misc devices. Expensive upgrade when you add all the wire I had to upsize for a 2000 watt inverter, but the batteries keep a charge for a really long time.
The devil is in the details in this kind of swap, and on the AC side it can get into quite a few things that are unexpected if you haven't done them before.
The Renogy appears to be a 65amp charger with 85% efficiency so would run on a 14ga input in most cases, but the Renegy also has a 30 amp automatic transfer switch so that it can be used to switch the full amount on shore power to the van when plugged in.
With that setup the unit would ideally be wired with the full shore power 30 amps directly to inverter charger and only go through a standalone automatic transfer switch first and have a generator..
The 120v output from the inverter would then go to the 120v fuse panel to be distributed both from the inverter and shore power, though the Renogy. It is also possible depending on how Roadtrek wired your van
If your Roadtrek had a 14ga wire to the charger, it most likely means that it is being powered by shore power from a breaker in the 120v breaker box. The breaker box would be powered from the shore power either directly to the box or through an automatic transfer switch that chooses shore or generator. It is also possible depending on how Roadtrek wired your van was wired that you have two AC inputs to the outlets in the van with only some of them inverter powered. That is how our 190 was wired. That would need to be corrected to run the whole van off the inverter.
Your system may be able to overload things wired a way that could cause other wires to fry also, or you could get into a double neutral to ground issue when plugged in to shore power or on generator.
More information really is needed to determine if what you have is a good idea or not at this point. Important information would start with how many AC cables went to old Tripplite and what size wire they were, plus what the Tripplite outlets powered.
You have multiple sources that are high enough powered to cause some hazard. Shore, generator if you have one, lithium batteries, the inverter, and the power from the alternator.
Our 2007 190P Chevy had the Tripplite and it took a lot of rewiring to get it all as it should be to be safe and reliable. We have 618ah of lithium, 2000watt 100amp charge Magnum inverter charger, stand alone second alternator controlled by a Wakespeed remote regulator, 300 watts of solar, no generator any more as we removed it. Not all that different from what you have described.