Trust lineup would probably be Monberaux, Ulmia, Qultada, Kupofried, and ??? (taking suggestions).
Rainmard is a option if you want him to take over frazzle and distract duty, I'm not sure if or how much weaker it is compared to a real RDM. Doesn't add anything to your setup but removing 1-2 casts from your rotation saves time during which you can deal damage and it's convenient since it gets annyoing having to cast that stuff over and over.
A skillchain partner could make sense. Naja Salaheem (UC), maybe Mildaurion or Ayame (UC) but more likely regular Ayame could make sense. They have all relatively fast TP gain, with distract you might not even need prime marine stewpot for trust ACC to get them to hit reliably. There is also Blazing Wyrm and Lunar Wyrm mementos with 10% trust ACC and others with 5% if you have them.
Ayame (UC) and Naja Salaheem (UC) have a WS with additional effect def down. Ayame (UC) only tries to close your skillchains but iirc you can open with liquifaction so she should close with impaction for fusion which you then can follow up with savage for light, might be worth it on RDM.
Excenmille (S) opens with Stag's Call on engage which gives 15% haste, attack and matt and lasts 3 minutes with 5 minute recast. I'm not sure but I think the ability is reset after re-summoning, maybe he needs to die first though.
Ygnas also has a WS that grants 25% attack but his enlight might override your en-spell, not sure if that's relevant with Naegling main hand.