300,000 guys seem like a lot to abandon to vegetable farming in Rabaul's volcanic soil, GreyJoy. I know it (abandoning them) was done IRL, but could you evacuate by H6KL to the Marianas and start a slow drain to there?
300,000 men not only at Rabaul eh!? 300K are spread all over the isolated bases of PM, Milne, Buna, Rossell Is., Rennell Is., Russell Is., Munda, Shortland, Buka, Gasmata, Arawe, Lae, Kavieng, Manus etc....
I've already evacuated the most valuable units. Air HQs, Army HQs, naval base forces, some heavy AA units etc. The real loss is the 21st Division which defended Bouganville and which is left there with no chances to airlift it out. Oh well, we'll do without.
I know it's a lot of troops. Especially a lot of SNLF units... I'll try to move out what i can, but in mid 1943 the Japs only have 54 H6KLs...not more... so you have to make a choice.
Rabaul? Yes, he can conquer it if he wants. It will take him some time but he can. If i was him i'd simply bypass it and go for Kavieng and Manus...much more easy.
Truk is full of troops now. 25K men out of 25K...I have moved there an air HQ and several AA units. The plan is to make it a tough nut to crack for his 4Es once they have conquered Kavieng. As long as Truk remains strong, the threat on his flank will be high.