As was stated, walk on roofs on a Sunline travel trailer were special order. It is not impossible, but most likely yours is not a walk on roof. That has not stopped some repairmen however from walking on the rafters which is not a correct way of doing this.
You can feel the difference of an actual walk on roof from the standard "non" walk on Sunline roof. And you will go right through a non walk on roof if your weight is off of a rafter.
The walk on, has 3/8 OSB board over half or all of the roof. It is solid between the rafters.
The "non" has a heavy thick corrugate backing (called bud board officially, some call it cardboard) that the rubber is glued too and then draped over the rafters. It is not intended to be used as a direct walk on surface. The feel is very different then the solid rafter feel ever 16".
See here. This is from a recent roof replacement.
The bud board folded back. You can see the rafters running left to right that the bud board was laying over.
Here is the bud board rolled up on the ground
And the roof after the bud board and rubber is removed. As you can see, it will not support you between the rafters.
To service items on the roof, as Mack stated, place a tarp or something soft to protect abrasion on the rubber surface. Then using small size pieces of plywood, 3/8 to 3/4" what ever you have and can easily lift, to span the 16" on center rafters. I use 1/2" thick, 2ft x 4ft sheets. Easy enough to lift up and can span several rafters in the 4 foot direction. I use a canvas or felt backed heavy car vinyl covering to protect the rubber.
And a must, is a stable ladder firmly planted on the ground. When your weight shifts off the ladder to the roof, and back onto it, that is one of the most tipping situations to be cautious of the ladder does not kick out.
Good luck and hope this helps. While you are up there, look at the caulking for "any" hair line or larger splits in "any" of the caulking. Once you see them, "now" is the time to correct them.
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Happy camping this year in your new Sunny and welcome to the club. We are glad to help and answer any and all questions.
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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