I haven got a clue when it comes to electrics I'll be getting an auto electrician to do it all. things have changes a lot since I did our last camper 8 years agoThey charge great off a dc-dc charger. I've got the 100ah renogy but after fitting the fogstar in a friend's van I'd choose the Fogstar given the choice again.
You can save some money on the dc-dc charger by buying the non-smart renogy 40 amp for about £120 and running it at 20A (fogstar don't recommend 40a for the 105)
You'll get sufficient charging info from the fogstar app.
Although most people on here seem to be using the new Victron XS 50a which you can run at 30A. A pricier but no doubt better option.
There are other things to consider with the battery pack option you mention. They do of course have a built in inverter so you have 240v without the need to buy and wire in an inverter into your van. However, the cheaper power packs wont be able to power things such as coffee machines or other power hungry items.