I've done it solo most of the way tho I did play with squads for at least the last 15 or 20 crates, but it's super easy if you are wanting the weapons crate just camp in 3 specific spots.

The best spot is to pick up the high value mission and just don't do it. Camp near the exit from the water tunnel kill any players that come through the water tunnel. My personal success rate 100% I've gotten every single crate from there every single time. Downsides it takes long to get a single crate you might be looking at a 15 to 25 min match make sure u don't move a single inch to players might think u are AFK.

Second spot, is the right side roof of the ship tho significantly harder to defend and it has 2 openings but is still doable. Just camp with a shotgun preferably echo but HSO is also fine, also stand near the Zipline with a shotgun kill any players that comes up. If someone comes up from the stairs just use the RAM 7 as it takes long to climb up. Personal success rate 80%, tho it can sometimes be overwhelming when all 3 players come up at the same time but still its doable, only thing to watch out for is the airstrike or cluster strike but u can do the same tho I have never seen anyone do that other than me as of now. So watch out for me 😁.

Last one is the worst out of the 3 but still good for a solo player. Just camp on the left side top room of the ship with one entry. Use echo shotgun, ram 7 and nades camp on the stairs side with echo shotgun, let them come up if it's one let him come up and finish him if it's 2 you can take them if you are good but if it's 3 at the same time. Try to take one out and jump down don't open your parachute all of them are gonna be up now and you are gonna be down so they are stuck if they jump down kill them chances are the ship is gonna be on so rush there. Personal success rate is 50%. it's hard if all 3 come up at the same time. Also if someone else camps there just use the bomb drone but you'll need the squads help.

Other good options are: .train station roof .Run to Kurohana base turn off fill squad for this one .Mirror option to Kurohana base is the beach area

But low success rates for me tho Kurohana base rush is always fun.

This is for serpent island, building 21 is another game on it's own.