Chris,
I thought everyone goes to Bunnies at least once per month!
Been there today, the Kincrome (not Kingchrome) pelikan copies are still in stock for both sizes.
Yes the larger would be my choice, I gave you dimensions, I think your 400mm L lens should fit with camera and smaller bits.
Have you considered silicagel bags or better still Peter Lee HKG has desiccant packs with built-in heater (115-240 VAC requires a Japanese style female plug). HKD 90 approx AUD13 + shipping. I bought one with my QHY5 guider and other bits.
Happy Snapper-ing
, don't get your feet er camera wet,
David