Without base building the end game is nothing different to DayZ really which will just end up with a deathmatch game mode. I love looting and I'm someone a PvE player, I've had several 10+ hour characters and never found enough scrap metal to make more then 2 walls, I get bored of looting eventually though once I'm fully kitted out then I want to build a base to store more stuff in but it's next to impossible to do that especially when solo.
My suggestion is allow wood wall upgrades but have them weak as fuck, and possible able to shoot through them. It worked pretty well in DayZ epoch i believe why not use it here?