I have a 378 and replaced my shower water valve through the 4” access port with absolutely no problem what-so-ever. The water lines have a 90 degree fitting and a rubber cone compression washer. Finger tight is all that is required. Had more trouble getting the lock nuts off the old valve.
I did silicon the backing plate of the new valve, put a bit of pipe thread putty on the new valve stems and installed. Whole job about 15 minutes. No leaks and that’s been about 3 yers ago.
JimF, CWO, US Army Ret, 100% DAV
2011 Georgetown 378TS
2008 Dodge Caliber Toad