Warm-Up: I camped this spell at H-11 in Wajaom Woodlands, around level 68. This is a common BST leveling spot, but there happens to be a Mamool in a little niche there (along with a raptor). Be careful when pulling the mamool, you don't want to aggro the raptor. There are plenty of pets to use; I recommend the attercops, but you can use pephredos in a pinch. You could even Charm puks if you are daring. But I would stick with attercops (be careful, they link). I simply put pet after pet on the Mamool until the Mamool is nearly dead, THEN I finish it off in hopes of learning the spell. It is best if you put a very large distance between yourself and the Mamool when you are getting ready to charm a new pet, this will allow you more time to recharm if your charm fails. Also, keeping Zephyr Mantle up (casting outside of hate range of the Mamool) is highly recommended.
Firespit: For this spell I camped in Wajaom Woodlands, the specific coordinates I don't recall, but it was in the southwestern part of the map (around the Mamook entrance). I was around level 68, and to be honest, I don't remember what pets I used, but I'm positive there are easily charmable ones spread throughout there (possibly treant saplings, attercops, etc.). But I pretty much followed the same procedure as with learning Warm-Up. Be careful of pulling the mage type mamools because this area has a high density of mamools, and you would not want to link any.
Diamondhide: This spell I camped in Bhaflau Thickets at level 70. It is likely possible to solo without Leave, but you may need to charm Tigers as well, if you run out of leeches (Tigers have some charm resistance, which increases the risk of doing this). I pulled trolls from F-9 and brought them to G-8. Using leech pets, I was able to slowly deplete the Troll's HP. However, it could take a long time to kill because of continuous use of Diamondhide. Not to mention the troll I was fighting was a PLD, and could cure itself.
Voracious Trunk: Learning this spell solo is perhaps the most challenging, and quite risky. I believe I was level 73 or so when I did it. Having Leave is essential for soloing this spell, because otherwise you will run out of pets. What I did was equipped at least two high damage spells (Hysteric Barrage, Disseverment, Frenetic Rip). In addition, I equipped the auto-refresh trait and also used a Vermillion cloak with MP refresh Sanction. This is because you have very little opportunity to rest MP while soloing this spell. You may want to consider equipping a sleep spell or two, as well, just in case something goes wrong. You can try learning this spell at basically any of the pond areas in Wajaom or Bhaflau that has leeches to charm.
Now as for the procedure of fighting the marids, I would charm a pet and sic it on a Marid (make sure it is not a Grand Marid, because other marids will link with it). You will notice that your pet is going to be killed quickly by the powerful marid. Be ready to Leave your current pet, charm a new pet, and put it on the Marid immediately. Do not let your pet die or you will likely run out of pets to put on the Marid. Always have Zephyr Mantle up (run out of hate range to recast it), because the Marids hit pretty hard. And for the first 5 or 6 times the Marid performs a TP attack, it will spawn a Chigoe which will immediately come after you. This is why you equip 2 high damage, quick casting spells. The Chigoe should die in one or two casts. And after 5 or 6 chigoes have spawned, you won't have to worry about anymore spawning when the Marid performs a TP attack. Note that the hate line here will be incredibly fickle. You do not want to gain any hate other than by putting your pet onto the Marid. A lot of times the Marid would take a swing at me during the whole ordeal (which is why Zephyr Mantle will be useful).