Additional benefits of the type 4 mount in conjunctions with the new Subal housings is the port lock (the absence of a port lock for older housings was supposed to be a weakness of Subal and caused some flooding experiences in the past...but not with me!)
When ordering a new housing (like the upcoming D4) I will probably switch to the type 4 and add some port3/4-adapters for my existing type3-ports and extension rings. Right now, they are in the process to make a new portadapter to be also used for the port-lock.
Although, the (existing and upcoming) port adapter does not fit the older DP-FE2 (older 8 inch domeport) -which I have- and thus I guess will have to switch this one as well...what a pity!
cheers!
