Drop in a Round Settings Device, don’t set a round number (keep the first setting unticked) to make this for all rounds.
Then tick the Override Keep Items Between Rounds setting
and tick the Keep Items Between Rounds.
There is also in the advanced settings Keep Resources Between Rounds -1.0 is don’t override and 0 to 1 is percentage kept, last time I heard this was not working properly, hope its fixed since then.
There is also the reload and restock weapon setting here.
that should be it, hopefully it works.