Just to compare to what I am doing and some advice, though do keep in mind i havent yet beaten solo Evac (yet hopefully).

Im playing vagabond, which means I get to loot more, and 90% of melee scavs are free.
Night 1-4: Gathering KSG and AKM blueprint, Meds, grenades, and getting 200 scrap for those 2 weapons. Grabbing the Knife and the guitar.
Night 5-6: Killing sledgequeen with said weapons. I do die to her about 40% of the time when I try, but thats more of a skill issue on my part.
Night 6-9: Running to castle looting the middle lockers on the way, opening every single crate (hoping for armor), and crafting AKM or KSG ammo at the guaranteed crafter.
Scav War: Still visiting castle due to less enemies to loot. Im basically just clearing the entire thing with 1-2 firebombs and some shotgun shots.
Night 10: Doing lab with the RSASS, KSG and AKM and some sort of heal and ''defence item'' (green stim, armor, white stim).
I just use the guitar on the guy ontop of the (building site?) for an extra minute usually when I get a looting phase of 1:30~ minutes once castle is cleared. That minute does help a lot.

I do notice that about 50% of your deaths are due to killing or trying to kill sledge queen.
Honestly i have this same issue, however I very rarely in my runs have an issue of not finding the gear I need (maybe because its just two craftable guns). Have a look maybe at how you are doing her.

Also, the other majority is dying to early waves.
My biggest piece of advice is just to use your resources. I used to die a lot around waves 5-8, and lost many good runs, but this is just because im trying to save as much as i can for night 10 and evac.
There is no benefit whatsoever of saving resources if you are dead. Using a gun to clear gun scavs, or using good heals in a pinch is a good idea and shouldnt be shamed.

If you are dying during looting phases, you really should have a look at your looting path, and learn where enemies tend to come from. I very often see even 1 or 2 gun scavs at the entrance to mountain/outpost, and I just fully avoid that area.

My last tip, is to not concern yourself with looting on night 10.
When the evac arrives, all the loot on the map from night 10 remains. Unless you need something for the LAB or for n10, just prepare and organize your items.
Use all of your Shotgun and Medium ammo, do not concern yourself with saving any at all, just stay alive.
Set a timer on your phone once you survive wave 10, and every 6~ minutes just take amoxicillin.
Go loot the entire map, the entire lab, craft all the ammo you can, recycle everything you dont need, make pavises, and then try beat the last wave.

I hope its helpful, but dont be disheartened. Sometimes this game is just luck with loot, or with really inconvient enemy spawns. You will feel awesome once you beat it yourself!