So I'm not sure 30A at the front fuse box is a good fuse size - might need 15A at the fuse box???
I would fuse the front at 20 amps for two reasons. The set up in the back is breaker is 15 amps. I'm not sure what your wire size is, looks like it's 12 or 10 gauge which is good. By going slightly higher with the feed fuse you avoid nuisance fuse blows which could come at a bad time. The idea behind the fuse up front is to protect the long feed wire from starting a fire if it were damaged and shorted (of course). So there is no reason to go larger than needed. In a pinch type short situation a 30 amp will take longer to blow. Maybe enough longer to start that fire we wish to avoid.
I likely didn't need to pull my positive wire out for the trip to the dealer. I just know dealers all too well and any modification whatsoever can be cause for them to not honor warranty issues. Sure, with a fight you can usually get them to acquiesce and honor the warranty. Life has too many fights already. As a safety issue, the main power lead from the OBC to the 12 volt is fused at the battery (up front) which means that the DC to DC converter in the OBC is protected from over current situations internally. So it is safe to connect another reasonable load to it (50 amps or less). Like you seem to intend to, I only use my set up to charge/run other items while the car is charging. This pretty well insures that there will not be high 12 volt loads in other OEM systems of the car which could approach the limits of the OBC's ability to supply them when added to the auxiliary non OEM system added.