RV Repair: Roof replacement; section, class c rv, rubber roofs

Question
I have an old 1978 midas class c rv 21'.  The roof was drooping a little last year and my brother coated it but I don't believe the coating held as the roof has dropped another 1/2" and the wood above is seperating as the plywood is degrading.  

This is about a 4' X 6' area and close to the air conditioner.  I am trying to find information on how to replace a roof section like this and can't seem to find what I am looking for.

I think I can do it but I am not confident with it without the proper knowledge and also I am not confident that the roof will hold me if I was on it right now.

Thanks for any info or links that you can provide,

Frank Kronstein

Answer
First of all, brace the roof from the inside by making "stilts" from 2x4's and 1/2" plywood( similar to holding a piee of drywall up while you nail it). That way you can crawl around on the roof without fear of it collasping on you. Then remove the air-conditioner. I don't know what kind of roof material you have. I'm guessing that in '78 it would have been a metal roof as opposed to the rubber roofs they use nowadays. If that is the case, then you need to remove the complete metal roof to see what the problem is underneath. To do that you will need to remove the trim around the edge of the roof, and it is probably stapled under that.
With out actually seeing what you have, it's hard to help you too much, but this should be a start. I'm guessing that there are some rotten decking and rafters. If you have the roof removed, you may want to just go ahead and replace everything that is looking bad.
Let me know if this helps, or don't hesitate to ask me more questions while you are repairing it.
Dave