If you treat the metal roof like we do the Sunline rubber roof setup, you should be able to service the roof.
I have not personally yet been on a Sunline metal roof however I have on other brands of camper. I treat the metal roof setup the same as a rubber roof as I'm almost sure Sunline did not out 3/8" decking under their metal roofs unless special ordered. A fellow forum member of one of our metal roofs can help confirm.
The issue is the concentrated amount of weight on one foot print between the rafters with that kind of weight can damage the roof and possibly break through. The key is spreading the weight out.
I start with putting down canvas, old carpet or tarp of sorts to protect the roof from abrasion. Even on a metal roof.
Then I use several 2 ft x 4 ft long sheets of plywood placed on top to span the rafters. That size is something I can man handle up there and move around. You and have it larger, just make sure it is wide enough to span the rafters and not shift off from wiggling around. Thickness can be 3/8 to 3/4" whatever you have around.
See here servicing my AC unit.
A heads up, make sure you have a solid ladder on a stable surface. The danger spot is transitioning from the ladder to the roof and visa versa. The ladder kicking out or you losing your balance is not good. I have not had a problem but I can feel my body weight shift and the ladder movement that could happen that high up to know, this is the caution spot.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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