I would suggest looking at the inside of a Trails West Campster
, it has an inside fiberglassed reinforced tee which works well, In my Astro, the manufacturer handled the same issue differently...it has four 6 inch wide corrugations molded into the roof, this created 4 extroverted channels running across the roof line to the front window of the trailer, the two outside channels turn the corner at the front dropping to the belly band reinforcing the front window area.
Personally, in a 13 foot Scamp
/ Acorn I took the trailer off the frame, flipped it upside down, I laid in the correct weight
of fiberglass cloth, using a carbon fiber cloth
crossing the weave three layers deep...Upside down the resin lays in place well, propping the trailer to maintain the correct curve of the shell relating to the roof takes a day before any pour and is very important. The four fiberglass units I have worked on were chop in mold created, great in theory but once a certain amount of damage occurs it loses considerable strength.
I am not a body shop, I just recently learned about the way Campster
handled their roof issues by picking one up, I learn everyday, the fiberglass experience I have is from fishing boats mainly...its been helpful, but I have had to be creative with trailer designs changing my thinking to specific stress points unlike water craft.
More people will weigh in here, research your options, post ideas, pick out what works for others and adapt. If you would like to see pics ask for them.
F.B.R.V. is a great place to get different views about the same issues.
I realize solutions are not right or wrong for me, they are more effective or less applicable to my particular issues in degrees of being effective...so first understand what your dealing with...really grasp the issues...the roof is just not weak...know the why its weak so your choices are guided by that correct understanding.
I look forward to your pics.
Safe Camping, Happy Trails.