I have been thinking about some subwoofers.. And i think i
will save my 18" drivers untill i move to a house..

I may use the 2235H, was there a mass ring that lowered the
FS on the 2235 to 17HZ ? What are the parameters for that driver, and what is the cone kit called?

any suggestions regarding a cabinet for this one? it will be
filtered to operate below 60- 80hz to my K2 s9500

I tend to build corner placed boxes, x 4

and i guess the tuning freq would be the same as FS for the driver..

What would be the ultimate box volume and tuning and filling with an 2235 driver ?

to go as low as possible, and no more than 280 liters..