Being retired is GREAT ! Got some time to do some urgent maintenance to the Ob. When I built it 3-4 years ago I made the roof lightweight by using exterior ply panels with plenty of roof paint on them. But the weather has not been kind and they have a few leak issues, fortunately not in critical places but annoying.
So bought 5 x 2400 x .660 meter panels of UV resistant PVC corrugated roofing and secured them on top of the ply. Hardly noticeable weight gain ( I slide my roof halves apart by hand, very easy and simple ) and I've been able to engineer a better weather seal where the two meet in the middle.
Probably wouldn't stand up to some of the harsher conditions in Ausland but my location is pretty protected. No more wet carpet inside and it also gives an insulation gap layer on top for those hot days.
$104 and 3 hours work, well worth it.
Only problem is the panels came with 'Included Clouds'