We just took over a 1980 410 COmmander with good bones but as stated she was a floating condo two other questions... One it seems that the holding tank may be leaving a lingering smell (No poop) but chemical. It has not been pumped in a while and I wonder if I pump this and add chemical (Which and how much) and give this a good rinse will this lingering smell go away? Also, where do most of you find V berth replacement cushions? So you have them made by an upholstery shop or do you buy them from a specific vendor.
My 1973 410 had an aluminum holding tank. There were pin holes in the bottom of it. If yours is aluminum I would imagine it is leaking. Replaced mine with a plastic tank.
I switched over to biologic (beneficial bacteria not just enzymes) tank treatment instead of chemicals. Available on line, or at an RV store, or marine supply house. Similar to what you would do with a residential septic tanks system. So far so good. You might want to add some biologic remedy to your bilge if the tanks has been leaking.
Mine has bunk beds forward, not a v-birth. I would look for a company making custom mattresses for boats. I think they are out there.
Something else you may need to do is to replace the hoses in your sanitary system.
After a while the waste smell will permeate thru the hoses
A good upholstery shop can make custom v-berth cushions. I've had a few of these made. Essentially I had the shop take the existing cushion and add 3 more inches of foam to it for a total thickness of 7 inches. If you are really going to sleep on these cushions, make sure they are comfortable before you write the check and authorize construction of the cushions. Remember, the foam cushion materials really vary in hardness (or stiffness) Only your back & butt can tell the difference. Happy snooze time if that is really what you are going to use them for :-)
Cushions will have to be custom made - as Dick said make sure you get the right amount AND density of foam . Often you can reuse the original foam if it's in good condition - One of the things their doing now is using 2 layers of foam - the bottom high density and the top a lower density ( softer ) a good upholstery shop will let you lie on some raw foam to get the feel of it . Much of it depend on the amount of use and the size of the people ( kids vs large adults )
What a great idea and the're cheap