EPDM roof

Hopefully yours is aluminum framed like mine is, that's the only reason why it didn't completely collapse, haha those AC units are up to 200lb. The contact cement has no reaction with the EPDM rubber and you can buy Liquid Rubber in 1 and 5 gallon cans in white as well. You could use a filler for your seams but I'm always weary of cracking, hence the eternabond tape, it you go with the liner that would of course eliminate that issue.
From what I see in your pics, the repair is definitely worth doing. Another tip as well, I can't tell from the pics but often times with these older C's the weight of the AC unit will tend to sag your roof a bit especially after water damage, but even from just plain old metal fatigue if you have aluminum rafters. Other than having a cambered roof; which yours does not appear to have you can fix by elevating it with a sheet of 7/8's OSB or whatever you prefer. The AC wire harness should have plenty of wiggle room as your only adding an additional inch to elevate the unit above the water line should your nice new roof sag and pool once complete otherwise, been there done that. I used a full sheet of OSB and it worked fine. Sure it adds weight to rig but only 80lbs or so. Well worth it for a five year investment. Mines a 30' 1993 and my roof has done great since then and will last another five years no problem.

Another

Here is what I'm dealing with.
The blue chalk is the areas of decking that are shot. I can feel the rafters are still solid, but hope springs eternal.

yes, rhino linings, or at least the other one, is available in colors other than black.
bumpy

Thanks everyone for the ideas.
Does rhino liner come in other than black? Never thought of that but a black roof in Tn. Might be too hot. I like the ideA of getting local from roofing supplier, probably cheaper.
@ Dr. I will take you up on that offer soon. Appreciate it.
I figure 5 years this r. V will be in our lives. But I would like to repair as best is reasonable, even if just for the next guy too.
@eddie. That's some solid information there, thanks. I considered that stuff as it seems to be rubber roof in a can. But, by the time I replace rotted decking, I'm thinking 1/2 the roof is stripped already. I'm Not sure. I've never been a fan of shortcuts, always feeling it could have turned out better. I'm already anticipating the worst so if it's worse yet,,,,,,,,oh boy. I know it's gonna be bad. If it was a smaller area it would be a no brainer.

This is why I tell her no one is going to give her an estimate. There is no way know to until your deep into it.
1/4 ac ply is a good tip. Gonna use that one. Do you mean the contact cement? Isn't the roof glue water based? Contact cement isn't i don't think. Bad reaction with the rubber? Worth checking out. Your right that glue is $$$. I love the roller idea. Does the seam tape replace the need to "spackle" the seams of substrate with wood filler?
All great info guys keep it coming.
What is that other type of membrane roofing I reAD about on here. P O or something. Bumpy, more tear resistant. Can't search for it, don't know the name.
Is that a better option?

You can buy a paint on liquid roof EPDM product as well. I replaced my EPDM liner 5 years ago with a ducor liner. It was a straight up pain in arse, took me a lot longer than I thought and the water damage, like home construction is ALWAYs worse than it appears. If it were to do it all over again, I would have used the paint on product and save a poop load of time. But if your dead set on the liner, a few things may help:
1, RV luan is expensive, 1/4 finished ply worked well for me.
2, the AC gasket is reusable, no need to replace it unless damaged. My resealed just fine.
3, builders contact cement is just as good as the pricy ducor brand.
4, A solid wood kitchen flour roller worked great when applying the membrane.
5, be sure to replace all your vents and caps. The old ones are nasty don't remove too easily with out bending and damages the flanges.

The paint on products will last just as long and you can paint it right over the old liner (except where you have water damage of course. You also may want to consider using eternabond or the ducor equivalent tape along the seems where you replace your luan, expensive tape but well worth it. A buddy of mine use it on his project and it worked great on the new seams.

Check RV roof in Green Springs, FL or Rhino Roof for options. Not cheap, but warranted for 20 years. Base consideration is how long will the RV be kept. Roof options come in a wide range of quality, and price.

Dicor is sort of the standard. But there is probably other brands worth considering. Start calling roofing suppliers and ask for prices from them too.it is basically the same roll roofing material used in connercial applications.

fix the wooden parts then check out rhino lining, etc. for a decent fix.
bumpy

Several years ago I replaced the EPDM on a 22' 5th, along with the roof boards as about 2/3 of the roof boards were in bad condition due to leaks. If you want to PM me I will be glad to tell you how I did it.