[A/S] '69 Safari black water tank and rear bath floor renovation

[joytbrew@xxxxxxxxxxx]

I just purchased a '69 Safari and the holding tank bracket at the 
rear is completely rusted out. There's also a large section of the  
sheet metal housing rusted away.  The main frame rail is rusted, but 
seems servicible. The drop frame rail that holds the tank brace is 
also rusted through and must be replaced.
  
I've started the renovation by removing the toilet and the belly pan 
section under the holding tank.  Unfortunately, I don't know for sure 
what holds the tank in position from the top.  If the tank is only 
retained with the bottom braces, I'm lucky that the toilet held tight 
while I towed it home.  I'd welcome any suggestions and information 
regarding this project.  

Do the toilet hold down bolts also serve to hold the tank?

I hope the drain lines from the bathroom sink and tub as 
well as the galley sink enter the tank through one fitting.  Is/are 
the fitting(s) only a slip joint that will loosen when the tank drops 
out?

Has anyone added a gray water tank to a vintage trailer of similar 
size?  Is it practical?

The floor droopy along the back edge and has a gap of about 1/2 
inch.  Does the holding tank serve as the brace to hold the floor up, 
or does the plastic on these old trailers shrink?  I don't see any 
dry rot along the edge of the plywood.  

Guess this is enough to help get on with my project.

                            Thanks