Troubleshooting a minecart transfer system in Minecraft 1.18.2 Java

This is the minecart transfer system I've put together. A hopper minecart comes in on the top right, unloads into the barrel, then leaves. Another hopper minecart comes in from the left, down the slope, loads, then leaves.

The unloader works perfectly. The loader portion, however, has two issues. If I try to 'bury' this, so that stone/whatever is directly on the sides, it doesn't hold the minecart while loading; the powered rail is always powered. I'm not sure where the short is, but I'd guess it's back around the two redstone dust blocks.

Also, the hopper directly under the barrel gets locked whenever a minecart is not down at the bottom loading, so the chest doesn't fill from the barrel unless the chest is also being unloaded at that moment.

How can this design be improved to fix both issues? In a perfect setup, I'd like the barrel to drain everything into the chest, then when the hopper minecart arrives, the hopper under the barrel locks, the hopper minecart empties anything in the chest (or fills to capacity), then the minecart leaves (even if not 100% filled, if the chest wasn't full enough) and the hopper under the barrel unlocks. I'm also looking for it to be 1-wide tileable, or at lease able to be 'buried' without blocks directly on the sides shorting it.

EDIT: I just noticed that I accidentally removed a hopper before taking the screenshots. There should be a hopper pointing down under the barrel and over the chest.