Hello Steve !
Your sub looks great,have you thoght of one or 2 jet drives from graupner?
I use one on the Octura a modified Deep Dive VI sub and wow what performance! turns on a dime and has gobs of power with a standard 12 volt can motor directly coupled to the jet drive.Also there is no danger of breaking the props and the hull lines make it look like a true jet.
It turned my sub into an underwater jet ski without the loss of too much running time.The funest sub I have ever made.
Reversing is done like on boats with cups that divert the jet.a secound chanel would probably have to be used.
The 4 rudders are great looking but drag is a consideration for running time and if converted to a jet drive you wont need any rudders!.Vector directed thrust is very cool indeed.Maybe just scale down the rudders.
As for rolling the rudders are going to fight that as well,but try as i did to aileronize your wings/ planes and that realy makes a great rool depending on the size of planes and speed atained.
Wings from model aircraft make great diveplanes/rudders with builtin detail.
The X craft is on my ways soon and its prity big.It will be a jet drive also,as the very large and sleek Nubian Starliner from Star Wars.
WTC s made from Otterboxes and Pellican cases,cheap and wter tight to 100ft!
Have a great day Dave